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 * Copyright (c) 2010, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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package jdk.javadoc.internal.doclets.formats.html.markup;

import java.io.IOException;
import java.io.Writer;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;

import jdk.javadoc.internal.doclets.formats.html.markup.HtmlAttr.Role;
import jdk.javadoc.internal.doclets.toolkit.Content;
import jdk.javadoc.internal.doclets.toolkit.util.DocletConstants;

A tree node representing an HTML element, containing the name of the element, a collection of attributes, and content. Except where otherwise stated, all methods in this class will throw NullPointerException for any arguments that are null or that are arrays or collections that contain null. Many methods in this class return this, to enable a series of chained method calls on a single object. Terminology: An HTML element is typically composed of a start tag, some enclosed content and typically an end tag. The start tag contains any attributes for the element. See: HTML element.
 
This is NOT part of any supported API.
 If you write code that depends on this, you do so at your own risk.
 This code and its internal interfaces are subject to change or
 deletion without notice.
See Also:
WhatWG: Normal Elements
HTML 5.1: Elements/**
 * A tree node representing an HTML element, containing the name of the element,
 * a collection of attributes, and content.
 *
 * Except where otherwise stated, all methods in this class will throw
 * {@code NullPointerException} for any arguments that are {@code null}
 * or that are arrays or collections that contain {@code null}.
 *
 * Many methods in this class return {@code this}, to enable a series
 * of chained method calls on a single object.
 *
 * Terminology: An HTML element is typically composed of a start tag, some
 * enclosed content and typically an end tag. The start tag contains any
 * attributes for the element. See:
 * <a href="https://en.wikipedia.org/wiki/HTML_element">HTML element</a>.
 *
 *  <p><b>This is NOT part of any supported API.
 *  If you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 *
 * @see <a href="https://html.spec.whatwg.org/multipage/syntax.html#normal-elements">WhatWG: Normal Elements</a>
 * @see <a href="https://www.w3.org/TR/html51/syntax.html#writing-html-documents-elements">HTML 5.1: Elements</a>
 */
public class HtmlTree extends Content {

    
The name of the HTML element. This value is never null. /**
     * The name of the HTML element.
     * This value is never {@code null}.
     */
    public final TagName tagName;

    
The attributes for the HTML element. The keys and values in this map are never null. /**
     * The attributes for the HTML element.
     * The keys and values in this map are never {@code null}.
     */
    private Map<HtmlAttr, String> attrs = Map.of();

    
The enclosed content ("inner HTML") for this HTML element.
The items in this list are never null.
/**
     * The enclosed content ("inner HTML") for this HTML element.
     * The items in this list are never null.
     */
    private List<Content> content = List.of();

    
A sentinel value to explicitly indicate empty content.
/**
     * A sentinel value to explicitly indicate empty content.
     */
    public static final Content EMPTY = new StringContent("");

    
Creates an HTMLTree object representing an HTML element with the given name. 
Params:
tagName – the name/**
     * Creates an {@code HTMLTree} object representing an HTML element
     * with the given name.
     *
     * @param tagName the name
     */
    public HtmlTree(TagName tagName) {
        this.tagName = Objects.requireNonNull(tagName);
    }

    
Adds an attribute.
Params:
attrName –  the name of the attribute
attrValue – the value of the attribute
Returns:
this object/**
     * Adds an attribute.
     *
     * @param attrName  the name of the attribute
     * @param attrValue the value of the attribute
     * @return this object
     */
    public HtmlTree put(HtmlAttr attrName, String attrValue) {
        if (attrs.isEmpty())
            attrs = new LinkedHashMap<>(3);
        attrs.put(Objects.requireNonNull(attrName), Entity.escapeHtmlChars(attrValue));
        return this;
    }

    
Sets the id attribute. 
Params:
id – the value for the attribute
Returns:
this object/**
     * Sets the {@code id} attribute.
     *
     * @param id the value for the attribute
     * @return this object
     */
    public HtmlTree setId(String id) {
        return put(HtmlAttr.ID, id);
    }

    
Sets the title attribute. Any nested start or end tags in the content will be removed. 
Params:
body – the content for the title attribute
Returns:
this object/**
     * Sets the {@code title} attribute.
     * Any nested start or end tags in the content will be removed.
     *
     * @param body the content for the title attribute
     * @return this object
     */
    public HtmlTree setTitle(Content body) {
        return put(HtmlAttr.TITLE, stripHtml(body));
    }

    
Sets the role attribute. 
Params:
role – the role
Returns:
this object/**
     * Sets the {@code role} attribute.
     *
     * @param role the role
     * @return this object
     */
    public HtmlTree setRole(Role role) {
        return put(HtmlAttr.ROLE, role.toString());
    }

    
Sets the class attribute. 
Params:
style – the value for the attribute
Returns:
this object/**
     * Sets the {@code class} attribute.
     *
     * @param style the value for the attribute
     * @return this object
     */
    public HtmlTree setStyle(HtmlStyle style) {
        return put(HtmlAttr.CLASS, style.cssName());
    }

    
Adds additional content for the HTML element.
Params:
content – the content/**
     * Adds additional content for the HTML element.
     *
     * @param content the content
     */
    @Override
    public HtmlTree add(Content content) {
        if (content instanceof ContentBuilder) {
            ((ContentBuilder) content).contents.forEach(this::add);
        }
        else if (content == HtmlTree.EMPTY || content.isValid()) {
            // quietly avoid adding empty or invalid nodes (except EMPTY)
            if (this.content.isEmpty())
                this.content = new ArrayList<>();
            this.content.add(content);
        }
        return this;
    }

    
Adds text content for the HTML element. If the last content member that was added is a StringContent, appends the string to that item; otherwise, creates and uses a new StringContent for the new text content. 
Params:
stringContent – string content that needs to be added/**
     * Adds text content for the HTML element.
     *
     * If the last content member that was added is a {@code StringContent},
     * appends the string to that item; otherwise, creates and uses a new {@code StringContent}
     * for the new text content.
     *
     * @param stringContent string content that needs to be added
     */
    @Override
    public HtmlTree add(CharSequence stringContent) {
        if (!content.isEmpty()) {
            Content lastContent = content.get(content.size() - 1);
            if (lastContent instanceof StringContent)
                lastContent.add(stringContent);
            else {
                add(new StringContent(stringContent));
            }
        }
        else {
            add(new StringContent(stringContent));
        }
        return this;
    }

    
Adds each of a list of content items.
Params:
list – the list
Returns:
this object/**
     * Adds each of a list of content items.
     *
     * @param list the list
     * @return this object
     */
    public HtmlTree add(List<? extends Content> list) {
        list.forEach(this::add);
        return this;
    }

    @Override
    public int charCount() {
        int n = 0;
        for (Content c : content) {
            n += c.charCount();
        }
        return n;
    }

    /*
     * The sets of ASCII URI characters to be left unencoded.
     * See "Uniform Resource Identifier (URI): Generic Syntax"
     * IETF RFC 3986. https://tools.ietf.org/html/rfc3986
     */
    public static final BitSet MAIN_CHARS;
    public static final BitSet QUERY_FRAGMENT_CHARS;

    static {
        BitSet alphaDigit = bitSet(bitSet('A', 'Z'), bitSet('a', 'z'), bitSet('0', '9'));
        BitSet unreserved = bitSet(alphaDigit, bitSet("-._~"));
        BitSet genDelims = bitSet(":/?#[]@");
        BitSet subDelims = bitSet("!$&'()*+,;=");
        MAIN_CHARS = bitSet(unreserved, genDelims, subDelims);
        BitSet pchar = bitSet(unreserved, subDelims, bitSet(":@"));
        QUERY_FRAGMENT_CHARS = bitSet(pchar, bitSet("/?"));
    }

    private static BitSet bitSet(String s) {
        BitSet result = new BitSet();
        for (int i = 0; i < s.length(); i++) {
           result.set(s.charAt(i));
        }
        return result;
    }

    private static BitSet bitSet(char from, char to) {
        BitSet result = new BitSet();
        result.set(from, to + 1);
        return result;
    }

    private static BitSet bitSet(BitSet... sets) {
        BitSet result = new BitSet();
        for (BitSet set : sets) {
            result.or(set);
        }
        return result;
    }

    
Apply percent-encoding to a URL. This is similar to URLEncoder but is less aggressive about encoding some characters, like '(', ')', ',' which are used in the anchor names for Java methods in HTML5 mode. 
Params:
url – the url to be percent-encoded.
Returns:
a percent-encoded string./**
     * Apply percent-encoding to a URL.
     * This is similar to {@link java.net.URLEncoder} but
     * is less aggressive about encoding some characters,
     * like '(', ')', ',' which are used in the anchor
     * names for Java methods in HTML5 mode.
     *
     * @param url the url to be percent-encoded.
     * @return a percent-encoded string.
     */
    public static String encodeURL(String url) {
        BitSet nonEncodingChars = MAIN_CHARS;
        StringBuilder sb = new StringBuilder();
        for (byte c : url.getBytes(StandardCharsets.UTF_8)) {
            if (c == '?' || c == '#') {
                sb.append((char) c);
                // switch to the more restrictive set inside
                // the query and/or fragment
                nonEncodingChars = QUERY_FRAGMENT_CHARS;
            } else if (nonEncodingChars.get(c & 0xFF)) {
                sb.append((char) c);
            } else {
                sb.append(String.format("%%%02X", c & 0xFF));
            }
        }
        return sb.toString();
    }

    
Creates an HTML A element. 
Params:
ref – the value for the href attribute}
body – the content for element
Returns:
the element/**
     * Creates an HTML {@code A} element.
     *
     * @param ref the value for the {@code href} attribute}
     * @param body the content for element
     * @return the element
     */
    public static HtmlTree A(String ref, Content body) {
        return new HtmlTree(TagName.A)
                .put(HtmlAttr.HREF, encodeURL(ref))
                .add(body);
    }

    
Creates an HTML CAPTION element with the given content. 
Params:
body – content for the element
Returns:
the element/**
     * Creates an HTML {@code CAPTION} element with the given content.
     *
     * @param body content for the element
     * @return the element
     */
    public static HtmlTree CAPTION(Content body) {
        return new HtmlTree(TagName.CAPTION)
                .add(body);
    }

    
Creates an HTML CODE element with the given content. 
Params:
body – content for the element
Returns:
the element/**
     * Creates an HTML {@code CODE} element with the given content.
     *
     * @param body content for the element
     * @return the element
     */
    public static HtmlTree CODE(Content body) {
        return new HtmlTree(TagName.CODE)
                .add(body);
    }

    
Creates an HTML DD element with the given content. 
Params:
body – content for the element
Returns:
the element/**
     * Creates an HTML {@code DD} element with the given content.
     *
     * @param body content for the element
     * @return the element
     */
    public static HtmlTree DD(Content body) {
        return new HtmlTree(TagName.DD)
                .add(body);
    }

    
Creates an HTML DL element with the given style. 
Params:
style – the style
Returns:
the element/**
     * Creates an HTML {@code DL} element with the given style.
     *
     * @param style the style
     * @return the element
     */
    public static HtmlTree DL(HtmlStyle style) {
        return new HtmlTree(TagName.DL)
                .setStyle(style);
    }

    
Creates an HTML DL element with the given style and content. 
Params:
style – the style
body –  the content
Returns:
the element/**
     * Creates an HTML {@code DL} element with the given style and content.
     *
     * @param style the style
     * @param body  the content
     * @return the element
     */
    public static HtmlTree DL(HtmlStyle style, Content body) {
        return new HtmlTree(TagName.DL)
                .setStyle(style)
                .add(body);
    }

    
Creates an HTML DIV element with the given style. 
Params:
style – the style
Returns:
the element/**
     * Creates an HTML {@code DIV} element with the given style.
     *
     * @param style the style
     * @return the element
     */
    public static HtmlTree DIV(HtmlStyle style) {
        return new HtmlTree(TagName.DIV)
                .setStyle(style);
    }

    
Creates an HTML DIV element with the given style and content. 
Params:
style – the style
body –  the content
Returns:
the element/**
     * Creates an HTML {@code DIV} element with the given style and content.
     *
     * @param style the style
     * @param body  the content
     * @return the element
     */
    public static HtmlTree DIV(HtmlStyle style, Content body) {
        return new HtmlTree(TagName.DIV)
                .setStyle(style)
                .add(body);
    }

    
Creates an HTML DIV element with the given content. 
Params:
body – the content
Returns:
the element/**
     * Creates an HTML {@code DIV} element with the given content.
     *
     * @param body the content
     * @return the element
     */
    public static HtmlTree DIV(Content body) {
        return new HtmlTree(TagName.DIV)
                .add(body);
    }

    
Creates an HTML DT element with the given content. 
Params:
body – the content
Returns:
the element/**
     * Creates an HTML {@code DT} element with the given content.
     *
     * @param body the content
     * @return the element
     */
    public static HtmlTree DT(Content body) {
        return new HtmlTree(TagName.DT)
                .add(body);
    }

    
Creates an HTML FOOTER element. The role is set to contentinfo. 
Returns:
the element/**
     * Creates an HTML {@code FOOTER} element.
     * The role is set to {@code contentinfo}.
     *
     * @return the element
     */
    public static HtmlTree FOOTER() {
        return new HtmlTree(TagName.FOOTER)
                .setRole(Role.CONTENTINFO);
    }

    
Creates an HTML HEADER element. The role is set to banner. 
Returns:
the element/**
     * Creates an HTML {@code HEADER} element.
     * The role is set to {@code banner}.
     *
     * @return the element
     */
    public static HtmlTree HEADER() {
        return new HtmlTree(TagName.HEADER)
                .setRole(Role.BANNER);
    }

    
Creates an HTML heading element with the given content.
Params:
headingTag – the tag for the heading
body –       the content
Returns:
the element/**
     * Creates an HTML heading element with the given content.
     *
     * @param headingTag the tag for the heading
     * @param body       the content
     * @return the element
     */
    public static HtmlTree HEADING(TagName headingTag, Content body) {
        return new HtmlTree(checkHeading(headingTag))
                .add(body);
    }

    
Creates an HTML heading element with the given style and content.
Params:
headingTag – the tag for the heading
style –      the stylesheet class
body –       the content
Returns:
the element/**
     * Creates an HTML heading element with the given style and content.
     *
     * @param headingTag the tag for the heading
     * @param style      the stylesheet class
     * @param body       the content
     * @return the element
     */
    public static HtmlTree HEADING(TagName headingTag, HtmlStyle style, Content body) {
        return new HtmlTree(checkHeading(headingTag))
                .setStyle(style)
                .add(body);
    }

    
Creates an HTML heading element with the given style and content. The title attribute is set from the content. 
Params:
headingTag – the tag for the heading
style –      the stylesheet class
body –       the content
Returns:
the element/**
     * Creates an HTML heading element with the given style and content.
     * The {@code title} attribute is set from the content.
     *
     * @param headingTag the tag for the heading
     * @param style      the stylesheet class
     * @param body       the content
     * @return the element
     */
    public static HtmlTree HEADING_TITLE(TagName headingTag,
                                         HtmlStyle style, Content body) {
        return new HtmlTree(checkHeading(headingTag))
                .setTitle(body)
                .setStyle(style)
                .add(body);
    }

    
Creates an HTML heading element with the given style and content. The title attribute is set from the content. 
Params:
headingTag – the tag for the heading
body –       the content
Returns:
the element/**
     * Creates an HTML heading element with the given style and content.
     * The {@code title} attribute is set from the content.
     *
     * @param headingTag the tag for the heading
     * @param body       the content
     * @return the element
     */
    public static HtmlTree HEADING_TITLE(TagName headingTag, Content body) {
        return new HtmlTree(checkHeading(headingTag))
                .setTitle(body)
                .add(body);
    }

    private static TagName checkHeading(TagName headingTag) {
        switch (headingTag) {
            case H1: case H2: case H3: case H4: case H5: case H6:
                return headingTag;
            default:
                throw new IllegalArgumentException(headingTag.toString());
        }
    }

    
Craetes an HTML HTML element with the given lang attribute, and HEAD and BODY contents. 
Params:
lang – the value for the lang attribute
head – the HEAD element
body – the BODY element
Returns:
the HTML element/**
     * Craetes an HTML {@code HTML} element with the given {@code lang} attribute,
     * and {@code HEAD} and {@code BODY} contents.
     *
     * @param lang the value for the {@code lang} attribute
     * @param head the {@code HEAD} element
     * @param body the {@code BODY} element
     * @return the {@code HTML} element
     */
    public static HtmlTree HTML(String lang, Content head, Content body) {
        return new HtmlTree(TagName.HTML)
                .put(HtmlAttr.LANG, lang)
                .add(head)
                .add(body);
    }

    
Creates an HTML INPUT element with the given id and initial value. The element as marked as initially disabled. 
Params:
type –  the type of input
id –    the id
value – the initial value
Returns:
the element/**
     * Creates an HTML {@code INPUT} element with the given id and initial value.
     * The element as marked as initially disabled.
     *
     * @param type  the type of input
     * @param id    the id
     * @param value the initial value
     * @return the element
     */
    public static HtmlTree INPUT(String type, String id, String value) {
        return new HtmlTree(TagName.INPUT)
                .put(HtmlAttr.TYPE, type)
                .put(HtmlAttr.ID, id)
                .put(HtmlAttr.VALUE, value)
                .put(HtmlAttr.DISABLED, "disabled");
    }

    
Creates an HTML LABEL element with the given content. 
Params:
forLabel – the value of the for attribute
body –     the content
Returns:
the element/**
     * Creates an HTML {@code LABEL} element with the given content.
     *
     * @param forLabel the value of the {@code for} attribute
     * @param body     the content
     * @return the element
     */
    public static HtmlTree LABEL(String forLabel, Content body) {
        return new HtmlTree(TagName.LABEL)
                .put(HtmlAttr.FOR, forLabel)
                .add(body);
    }

    
Creates an HTML LI element with the given content. 
Params:
body – the content
Returns:
the element/**
     * Creates an HTML {@code LI} element with the given content.
     *
     * @param body the content
     * @return the element
     */
    public static HtmlTree LI(Content body) {
        return new HtmlTree(TagName.LI)
                .add(body);
    }

    
Creates an HTML LI element with the given style and the given content. 
Params:
style – the style
body –  the content
Returns:
the element/**
     * Creates an HTML {@code LI} element with the given style and the given content.
     *
     * @param style the style
     * @param body  the content
     * @return the element
     */
    public static HtmlTree LI(HtmlStyle style, Content body) {
        return LI(body)
                .setStyle(style);
    }

    
Creates an HTML LINK tag with the given attributes. 
Params:
rel –  the relevance of the link: the rel attribute
type –  the type of link: the type attribute
href –  the path for the link: the href attribute
title – title for the link: the title attribute
Returns:
the element/**
     * Creates an HTML {@code LINK} tag with the given attributes.
     *
     * @param rel   the relevance of the link: the {@code rel} attribute
     * @param type  the type of link: the {@code type} attribute
     * @param href  the path for the link: the {@code href} attribute
     * @param title title for the link: the {@code title} attribute
     * @return the element
     */
    public static HtmlTree LINK(String rel, String type, String href, String title) {
        return new HtmlTree(TagName.LINK)
                .put(HtmlAttr.REL, rel)
                .put(HtmlAttr.TYPE, type)
                .put(HtmlAttr.HREF, href)
                .put(HtmlAttr.TITLE, title);
    }

    
Creates an HTML MAIN element. The role is set to main. 
Returns:
the element/**
     * Creates an HTML {@code MAIN} element.
     * The role is set to {@code main}.
     *
     * @return the element
     */
    public static HtmlTree MAIN() {
        return new HtmlTree(TagName.MAIN)
                .setRole(Role.MAIN);
    }

    
Creates an HTML MAIN element with the given content. The role is set to main. 
Returns:
the element/**
     * Creates an HTML {@code MAIN} element with the given content.
     * The role is set to {@code main}.
     *
     * @return the element
     */
    public static HtmlTree MAIN(Content body) {
        return new HtmlTree(TagName.MAIN)
                .setRole(Role.MAIN)
                .add(body);
    }

    
Creates an HTML META element with http-equiv and content attributes. 
Params:
httpEquiv – the value for the http-equiv attribute
content –  the type of content, to be used in the content attribute
charset –  the character set for the document, to be used in the content attribute
Returns:
the element/**
     * Creates an HTML {@code META} element with {@code http-equiv} and {@code content} attributes.
     *
     * @param httpEquiv the value for the {@code http-equiv} attribute
     * @param content   the type of content, to be used in the {@code content} attribute
     * @param charset   the character set for the document, to be used in the {@code content} attribute
     * @return the element
     */
    public static HtmlTree META(String httpEquiv, String content, String charset) {
        return new HtmlTree(TagName.META)
                .put(HtmlAttr.HTTP_EQUIV, httpEquiv)
                .put(HtmlAttr.CONTENT, content + "; charset=" + charset);
    }

    
Creates an HTML META element with name and content attributes. 
Params:
name –  the value for the name attribute
content – the value for the content attribute
Returns:
the element/**
     * Creates an HTML {@code META} element with {@code name} and {@code content} attributes.
     *
     * @param name    the value for the {@code name} attribute
     * @param content the value for the {@code content} attribute
     * @return the element
     */
    public static HtmlTree META(String name, String content) {
        return new HtmlTree(TagName.META)
                .put(HtmlAttr.NAME, name)
                .put(HtmlAttr.CONTENT, content);
    }

    
Creates an HTML NAV element. The role is set to navigation. 
Returns:
the element/**
     * Creates an HTML {@code NAV} element.
     * The role is set to {@code navigation}.
     *
     * @return the element
     */
    public static HtmlTree NAV() {
        return new HtmlTree(TagName.NAV)
                .setRole(Role.NAVIGATION);
    }

    
Creates an HTML NOSCRIPT element with some content. 
Params:
body – the content
Returns:
the element/**
     * Creates an HTML {@code NOSCRIPT} element with some content.
     *
     * @param body the content
     * @return the element
     */
    public static HtmlTree NOSCRIPT(Content body) {
        return new HtmlTree(TagName.NOSCRIPT)
                .add(body);
    }

    
Creates an HTML P element with some content. 
Params:
body – the content
Returns:
the element/**
     * Creates an HTML {@code P} element with some content.
     *
     * @param body the content
     * @return the element
     */
    public static HtmlTree P(Content body) {
        return new HtmlTree(TagName.P)
                .add(body);
    }

    
Creates an HTML P element with the given style and some content. 
Params:
style – the style
body –  the content
Returns:
the element/**
     * Creates an HTML {@code P} element with the given style and some content.
     *
     * @param style the style
     * @param body  the content
     * @return the element
     */
    public static HtmlTree P(HtmlStyle style, Content body) {
        return P(body)
                .setStyle(style);
    }

    
Creates an HTML SCRIPT element with some script content. The type of the script is set to text/javascript. 
Params:
src – the content
Returns:
the element/**
     * Creates an HTML {@code SCRIPT} element with some script content.
     * The type of the script is set to {@code text/javascript}.
     *
     * @param src the content
     * @return the element
     */
    public static HtmlTree SCRIPT(String src) {
        return new HtmlTree(TagName.SCRIPT)
                .put(HtmlAttr.TYPE, "text/javascript")
                .put(HtmlAttr.SRC, src);

    }

    
Creates an HTML SECTION element with the given style. 
Params:
style – the style
Returns:
the element/**
     * Creates an HTML {@code SECTION} element with the given style.
     *
     * @param style the style
     * @return the element
     */
    public static HtmlTree SECTION(HtmlStyle style) {
        return new HtmlTree(TagName.SECTION)
                .setStyle(style);
    }

    
Creates an HTML SECTION element with the given style and some content. 
Params:
style – the style
body –  the content
Returns:
the element/**
     * Creates an HTML {@code SECTION} element with the given style and some content.
     *
     * @param style the style
     * @param body  the content
     * @return the element
     */
    public static HtmlTree SECTION(HtmlStyle style, Content body) {
        return new HtmlTree(TagName.SECTION)
                .setStyle(style)
                .add(body);
    }

    
Creates an HTML SMALL element with some content. 
Params:
body –  the content
Returns:
the element/**
     * Creates an HTML {@code SMALL} element with some content.
     *
     * @param body  the content
     * @return the element
     */
    public static HtmlTree SMALL(Content body) {
        return new HtmlTree(TagName.SMALL)
                .add(body);
    }

    
Creates an HTML SPAN element with some content. 
Params:
body –  the content
Returns:
the element/**
     * Creates an HTML {@code SPAN} element with some content.
     *
     * @param body  the content
     * @return the element
     */
    public static HtmlTree SPAN(Content body) {
        return new HtmlTree(TagName.SPAN)
                .add(body);
    }

    
Creates an HTML SPAN element with the given style and some content. 
Params:
styleClass – the style
body –       the content
Returns:
the element/**
     * Creates an HTML {@code SPAN} element with the given style and some content.
     *
     * @param styleClass the style
     * @param body       the content
     * @return the element
     */
    public static HtmlTree SPAN(HtmlStyle styleClass, Content body) {
        return SPAN(body)
                .setStyle(styleClass);
    }

    
Creates an HTML SPAN element with the given id and some content. 
Params:
id –    the id
body –  the content
Returns:
the element/**
     * Creates an HTML {@code SPAN} element with the given id and some content.
     *
     * @param id    the id
     * @param body  the content
     * @return the element
     */
    public static HtmlTree SPAN_ID(String id, Content body) {
        return new HtmlTree(TagName.SPAN)
                .setId(id)
                .add(body);
    }

    
Creates an HTML SPAN element with the given id and style, and some content. 
Params:
id –    the id
style – the style
body –  the content
Returns:
the element/**
     * Creates an HTML {@code SPAN} element with the given id and style, and some content.
     *
     * @param id    the id
     * @param style the style
     * @param body  the content
     * @return the element
     */
    public static HtmlTree SPAN(String id, HtmlStyle style, Content body) {
        return new HtmlTree(TagName.SPAN)
                .setId(id)
                .setStyle(style)
                .add(body);
    }

    
Creates an HTML TD element with the given style and some content. 
Params:
style – the style
body –  the content
Returns:
the element/**
     * Creates an HTML {@code TD} element with the given style and some content.
     *
     * @param style the style
     * @param body  the content
     * @return the element
     */
    public static HtmlTree TD(HtmlStyle style, Content body) {
        return new HtmlTree(TagName.TD)
                .setStyle(style)
                .add(body);
    }

    
Creates an HTML TH element with the given style and scope, and some content. 
Params:
style – the style
scope – the value for the scope attribute
body –  the content
Returns:
the element/**
     * Creates an HTML {@code TH} element with the given style and scope, and some content.
     *
     * @param style the style
     * @param scope the value for the {@code scope} attribute
     * @param body  the content
     * @return the element
     */
    public static HtmlTree TH(HtmlStyle style, String scope, Content body) {
        return new HtmlTree(TagName.TH)
                .setStyle(style)
                .put(HtmlAttr.SCOPE, scope)
                .add(body);
    }

    
Creates an HTML TH element with the given scope, and some content. 
Params:
scope – the value for the scope attribute
body –  the content
Returns:
the element/**
     * Creates an HTML {@code TH} element with the given scope, and some content.
     *
     * @param scope the value for the {@code scope} attribute
     * @param body  the content
     * @return the element
     */
    public static HtmlTree TH(String scope, Content body) {
        return new HtmlTree(TagName.TH)
                .put(HtmlAttr.SCOPE, scope)
                .add(body);
    }

    
Creates an HTML TITLE element with some content. 
Params:
body – the content
Returns:
the element/**
     * Creates an HTML {@code TITLE} element with some content.
     *
     * @param body the content
     * @return the element
     */
    public static HtmlTree TITLE(String body) {
        return new HtmlTree(TagName.TITLE)
            .add(body);
    }

    
Creates an HTML UL element with the given style and some content. 
Params:
style – the style
first – the initial content
more –  additional content
Returns:
the element/**
     * Creates an HTML {@code UL} element with the given style and some content.
     *
     * @param style the style
     * @param first the initial content
     * @param more  additional content
     * @return the element
     */
    public static HtmlTree UL(HtmlStyle style, Content first, Content... more) {
        HtmlTree htmlTree = new HtmlTree(TagName.UL)
                .setStyle(style);
        htmlTree.add(first);
        for (Content c : more) {
            htmlTree.add(c);
        }
        return htmlTree;
    }

    @Override
    public boolean isEmpty() {
        return (!hasContent() && !hasAttrs());
    }

    
Returns true if the HTML tree has content.
Returns:
true if the HTML tree has content else return false/**
     * Returns true if the HTML tree has content.
     *
     * @return true if the HTML tree has content else return false
     */
    public boolean hasContent() {
        return (!content.isEmpty());
    }

    
Returns true if the HTML tree has attributes.
Returns:
true if the HTML tree has attributes else return false/**
     * Returns true if the HTML tree has attributes.
     *
     * @return true if the HTML tree has attributes else return false
     */
    public boolean hasAttrs() {
        return (!attrs.isEmpty());
    }

    
Returns true if the HTML tree has a specific attribute.
Params:
attrName – name of the attribute to check within the HTML tree
Returns:
true if the HTML tree has the specified attribute else return false/**
     * Returns true if the HTML tree has a specific attribute.
     *
     * @param attrName name of the attribute to check within the HTML tree
     * @return true if the HTML tree has the specified attribute else return false
     */
    public boolean hasAttr(HtmlAttr attrName) {
        return (attrs.containsKey(attrName));
    }

    
Returns true if the HTML tree is valid. This check is more specific to
standard doclet and not exactly similar to W3C specifications. But it
ensures HTML validation.
Returns:
true if the HTML tree is valid/**
     * Returns true if the HTML tree is valid. This check is more specific to
     * standard doclet and not exactly similar to W3C specifications. But it
     * ensures HTML validation.
     *
     * @return true if the HTML tree is valid
     */
    @Override
    public boolean isValid() {
        switch (tagName) {
            case A:
                return (hasAttr(HtmlAttr.ID) || (hasAttr(HtmlAttr.HREF) && hasContent()));
            case BR:
                return (!hasContent() && (!hasAttrs() || hasAttr(HtmlAttr.CLEAR)));
            case HR:
            case INPUT:
                return (!hasContent());
            case IMG:
                return (hasAttr(HtmlAttr.SRC) && hasAttr(HtmlAttr.ALT) && !hasContent());
            case LINK:
                return (hasAttr(HtmlAttr.HREF) && !hasContent());
            case META:
                return (hasAttr(HtmlAttr.CONTENT) && !hasContent());
            case SCRIPT:
                return ((hasAttr(HtmlAttr.TYPE) && hasAttr(HtmlAttr.SRC) && !hasContent()) ||
                        (hasAttr(HtmlAttr.TYPE) && hasContent()));
            case SPAN:
                return (hasAttr(HtmlAttr.ID) || hasContent());
            default :
                return hasContent();
        }
    }

    
Returns true if the element is a normal element that is phrasing content.
See Also:
Phrasing Content
Returns:
true if the HTML tag is an inline element/**
     * Returns true if the element is a normal element that is <em>phrasing content</em>.
     *
     * @return true if the HTML tag is an inline element
     *
     * @see <a href="https://www.w3.org/TR/html51/dom.html#kinds-of-content-phrasing-content">Phrasing Content</a>
     */
    public boolean isInline() {
        switch (tagName) {
            case A: case BUTTON: case BR: case CODE: case EM: case I: case IMG:
            case LABEL: case SMALL: case SPAN: case STRONG: case SUB:
                return true;
            default:
                return false;
        }
    }

    
Returns whether or not this is a void element.
See Also:
Void Elements
Returns:
whether or not this is a void element/**
     * Returns whether or not this is a <em>void</em> element.
     *
     * @return whether or not this is a void element
     *
     * @see <a href="https://www.w3.org/TR/html51/syntax.html#void-elements">Void Elements</a>
     */
    public boolean isVoid() {
        switch (tagName) {
            case BR: case HR: case IMG: case INPUT: case LINK: case META:
                return true;
            default:
                return false;
        }
    }

    @Override
    public boolean write(Writer out, boolean atNewline) throws IOException {
        boolean isInline = isInline();
        if (!isInline && !atNewline)
            out.write(DocletConstants.NL);
        String tagString = tagName.toString();
        out.write("<");
        out.write(tagString);
        Iterator<HtmlAttr> iterator = attrs.keySet().iterator();
        HtmlAttr key;
        String value;
        while (iterator.hasNext()) {
            key = iterator.next();
            value = attrs.get(key);
            out.write(" ");
            out.write(key.toString());
            if (!value.isEmpty()) {
                out.write("=\"");
                out.write(value);
                out.write("\"");
            }
        }
        out.write(">");
        boolean nl = false;
        for (Content c : content)
            nl = c.write(out, nl);
        if (!isVoid()) {
            out.write("</");
            out.write(tagString);
            out.write(">");
        }
        if (!isInline) {
            out.write(DocletConstants.NL);
            return true;
        } else {
            return false;
        }
    }

    
Given a Content node, strips all html characters and
return the result.
Params:
body – The content node to check.
Returns:
the plain text from the content node/**
     * Given a Content node, strips all html characters and
     * return the result.
     *
     * @param body The content node to check.
     * @return the plain text from the content node
     *
     */
    private static String stripHtml(Content body) {
        String rawString = body.toString();
        // remove HTML tags
        rawString = rawString.replaceAll("<.*?>", " ");
        // consolidate multiple spaces between a word to a single space
        rawString = rawString.replaceAll("\\b\\s{2,}\\b", " ");
        // remove extra whitespaces
        return rawString.trim();
    }
}