https://github.com/JetBrains/java-annotations: A set of annotations used for code inspection support and code documentation. 
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 * Copyright 2000-2020 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
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 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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package org.intellij.lang.annotations;

import java.lang.annotation.*;


Specifies the replacement value for non-constant variables and method return values. This may help static analyzers to properly parse the concatenation of several values which is used in @Language or Pattern context. 

Example:

@Subst("Tahoma")
final String font = new JLabel().getFont().getName();
@Language("HTML")
String message = "<html><span style='font: " + font + "; font-size:smaller'>" 
  + ... + "</span></html>";



 Here the parser assumes that when font appears in the concatenation it's value is "Tahoma", so it can continue parsing the concatenation. 


See Also:
/**
 * Specifies the replacement value for non-constant variables and method return values.
 * This may help static analyzers to properly parse the concatenation of several values
 * which is used in @{@link Language} or {@link Pattern} context.
 * <p>
 * Example:
 * <pre>
 * &#64;Subst("Tahoma")
 * final String font = new JLabel().getFont().getName();
 * 
 * &#64;Language("HTML")
 * String message = "&lt;html&gt;&lt;span style='font: " + font + "; font-size:smaller'&gt;" 
 *   + ... + "&lt;/span&gt;&lt;/html&gt;";
 * </pre>
 * <p>
 * Here the parser assumes that when {@code font} appears in the concatenation it's value is {@code "Tahoma"},
 * so it can continue parsing the concatenation.
 * </p>
 * 
 * @see Language
 * @see Pattern
 */
@Retention(RetentionPolicy.CLASS)
@Target({ElementType.METHOD, ElementType.FIELD, ElementType.LOCAL_VARIABLE, ElementType.PARAMETER})
public @interface Subst {
    String value();
}