https://freemarker.apache.org/: FreeMarker is a "template engine"; a generic tool to generate text output based on templates. (Apache Software Foundation) 
class freemarker.core.BuiltInsForStringsBasic$substringBI$1 implements freemarker.template.TemplateMethodModelEx
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: freemarker.core.BuiltInsForStringsBasic$substringBI$1
  super_class: java.lang.Object
{
  final freemarker.core.BuiltInsForStringsBasic$substringBI this$1;
    descriptor: Lfreemarker/core/BuiltInsForStringsBasic$substringBI;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  private final java.lang.String val$s;
    descriptor: Ljava/lang/String;
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC

  void <init>(freemarker.core.BuiltInsForStringsBasic$substringBI, java.lang.String);
    descriptor: (Lfreemarker/core/BuiltInsForStringsBasic$substringBI;Ljava/lang/String;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=3, args_size=3
        start local 0 // freemarker.core.BuiltInsForStringsBasic$substringBI$1 this
         0: .line 583
            aload 0 /* this */
            aload 1
            putfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.this$1:Lfreemarker/core/BuiltInsForStringsBasic$substringBI;
            aload 0 /* this */
            aload 2
            putfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.val$s:Ljava/lang/String;
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
            return
        end local 0 // freemarker.core.BuiltInsForStringsBasic$substringBI$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lfreemarker/core/BuiltInsForStringsBasic$substringBI$1;
    MethodParameters:
        Name  Flags
      this$0  final
      val$s   final

  public java.lang.Object exec(java.util.List);
    descriptor: (Ljava/util/List;)Ljava/lang/Object;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=5, locals=6, args_size=2
        start local 0 // freemarker.core.BuiltInsForStringsBasic$substringBI$1 this
        start local 1 // java.util.List args
         0: .line 586
            aload 1 /* args */
            invokeinterface java.util.List.size:()I
            istore 2 /* argCount */
        start local 2 // int argCount
         1: .line 587
            aload 0 /* this */
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.this$1:Lfreemarker/core/BuiltInsForStringsBasic$substringBI;
            iload 2 /* argCount */
            iconst_1
            iconst_2
            invokevirtual freemarker.core.BuiltInsForStringsBasic$substringBI.checkMethodArgCount:(III)V
         2: .line 589
            aload 0 /* this */
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.this$1:Lfreemarker/core/BuiltInsForStringsBasic$substringBI;
            aload 1 /* args */
            iconst_0
            invokevirtual freemarker.core.BuiltInsForStringsBasic$substringBI.getNumberMethodArg:(Ljava/util/List;I)Ljava/lang/Number;
            invokevirtual java.lang.Number.intValue:()I
            istore 3 /* beginIdx */
        start local 3 // int beginIdx
         3: .line 591
            aload 0 /* this */
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.val$s:Ljava/lang/String;
            invokevirtual java.lang.String.length:()I
            istore 4 /* len */
        start local 4 // int len
         4: .line 593
            iload 3 /* beginIdx */
            ifge 6
         5: .line 594
            aload 0 /* this */
            iconst_0
            iload 3 /* beginIdx */
            invokevirtual freemarker.core.BuiltInsForStringsBasic$substringBI$1.newIndexLessThan0Exception:(II)Lfreemarker/template/TemplateModelException;
            athrow
         6: .line 595
      StackMap locals: int int int
      StackMap stack:
            iload 3 /* beginIdx */
            iload 4 /* len */
            if_icmple 8
         7: .line 596
            aload 0 /* this */
            iconst_0
            iload 3 /* beginIdx */
            iload 4 /* len */
            invokevirtual freemarker.core.BuiltInsForStringsBasic$substringBI$1.newIndexGreaterThanLengthException:(III)Lfreemarker/template/TemplateModelException;
            athrow
         8: .line 599
      StackMap locals:
      StackMap stack:
            iload 2 /* argCount */
            iconst_1
            if_icmple 21
         9: .line 600
            aload 0 /* this */
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.this$1:Lfreemarker/core/BuiltInsForStringsBasic$substringBI;
            aload 1 /* args */
            iconst_1
            invokevirtual freemarker.core.BuiltInsForStringsBasic$substringBI.getNumberMethodArg:(Ljava/util/List;I)Ljava/lang/Number;
            invokevirtual java.lang.Number.intValue:()I
            istore 5 /* endIdx */
        start local 5 // int endIdx
        10: .line 601
            iload 5 /* endIdx */
            ifge 12
        11: .line 602
            aload 0 /* this */
            iconst_1
            iload 5 /* endIdx */
            invokevirtual freemarker.core.BuiltInsForStringsBasic$substringBI$1.newIndexLessThan0Exception:(II)Lfreemarker/template/TemplateModelException;
            athrow
        12: .line 603
      StackMap locals: int
      StackMap stack:
            iload 5 /* endIdx */
            iload 4 /* len */
            if_icmple 14
        13: .line 604
            aload 0 /* this */
            iconst_1
            iload 5 /* endIdx */
            iload 4 /* len */
            invokevirtual freemarker.core.BuiltInsForStringsBasic$substringBI$1.newIndexGreaterThanLengthException:(III)Lfreemarker/template/TemplateModelException;
            athrow
        14: .line 606
      StackMap locals:
      StackMap stack:
            iload 3 /* beginIdx */
            iload 5 /* endIdx */
            if_icmple 20
        15: .line 607
            new java.lang.StringBuilder
            dup
            ldc "?"
            invokespecial java.lang.StringBuilder.<init>:(Ljava/lang/String;)V
            aload 0 /* this */
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.this$1:Lfreemarker/core/BuiltInsForStringsBasic$substringBI;
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI.key:Ljava/lang/String;
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
            invokevirtual java.lang.StringBuilder.toString:()Ljava/lang/String;
            iconst_5
            anewarray java.lang.Object
            dup
            iconst_0
        16: .line 608
            ldc "The begin index argument, "
            aastore
            dup
            iconst_1
            iload 3 /* beginIdx */
            invokestatic java.lang.Integer.valueOf:(I)Ljava/lang/Integer;
            aastore
            dup
            iconst_2
        17: .line 609
            ldc ", shouldn't be greater than the end index argument, "
            aastore
            dup
            iconst_3
        18: .line 610
            iload 5 /* endIdx */
            invokestatic java.lang.Integer.valueOf:(I)Ljava/lang/Integer;
            aastore
            dup
            iconst_4
            ldc "."
            aastore
        19: .line 607
            invokestatic freemarker.core._MessageUtil.newMethodArgsInvalidValueException:(Ljava/lang/String;[Ljava/lang/Object;)Lfreemarker/template/TemplateModelException;
            athrow
        20: .line 612
      StackMap locals:
      StackMap stack:
            new freemarker.template.SimpleScalar
            dup
            aload 0 /* this */
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.val$s:Ljava/lang/String;
            iload 3 /* beginIdx */
            iload 5 /* endIdx */
            invokevirtual java.lang.String.substring:(II)Ljava/lang/String;
            invokespecial freemarker.template.SimpleScalar.<init>:(Ljava/lang/String;)V
            areturn
        end local 5 // int endIdx
        21: .line 614
      StackMap locals:
      StackMap stack:
            new freemarker.template.SimpleScalar
            dup
            aload 0 /* this */
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.val$s:Ljava/lang/String;
            iload 3 /* beginIdx */
            invokevirtual java.lang.String.substring:(I)Ljava/lang/String;
            invokespecial freemarker.template.SimpleScalar.<init>:(Ljava/lang/String;)V
            areturn
        end local 4 // int len
        end local 3 // int beginIdx
        end local 2 // int argCount
        end local 1 // java.util.List args
        end local 0 // freemarker.core.BuiltInsForStringsBasic$substringBI$1 this
      LocalVariableTable:
        Start  End  Slot      Name  Signature
            0   22     0      this  Lfreemarker/core/BuiltInsForStringsBasic$substringBI$1;
            0   22     1      args  Ljava/util/List;
            1   22     2  argCount  I
            3   22     3  beginIdx  I
            4   22     4       len  I
           10   21     5    endIdx  I
    Exceptions:
      throws freemarker.template.TemplateModelException
    MethodParameters:
      Name  Flags
      args  

  private freemarker.template.TemplateModelException newIndexGreaterThanLengthException(int, int, int);
    descriptor: (III)Lfreemarker/template/TemplateModelException;
    flags: (0x0002) ACC_PRIVATE
    Code:
      stack=6, locals=4, args_size=4
        start local 0 // freemarker.core.BuiltInsForStringsBasic$substringBI$1 this
        start local 1 // int argIdx
        start local 2 // int idx
        start local 3 // int len
         0: .line 621
            new java.lang.StringBuilder
            dup
            ldc "?"
            invokespecial java.lang.StringBuilder.<init>:(Ljava/lang/String;)V
            aload 0 /* this */
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.this$1:Lfreemarker/core/BuiltInsForStringsBasic$substringBI;
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI.key:Ljava/lang/String;
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
            invokevirtual java.lang.StringBuilder.toString:()Ljava/lang/String;
            iload 1 /* argIdx */
            iconst_5
            anewarray java.lang.Object
            dup
            iconst_0
         1: .line 622
            ldc "The index mustn't be greater than the length of the string, "
            aastore
            dup
            iconst_1
         2: .line 623
            iload 3 /* len */
            invokestatic java.lang.Integer.valueOf:(I)Ljava/lang/Integer;
            aastore
            dup
            iconst_2
         3: .line 624
            ldc ", but it was "
            aastore
            dup
            iconst_3
            iload 2 /* idx */
            invokestatic java.lang.Integer.valueOf:(I)Ljava/lang/Integer;
            aastore
            dup
            iconst_4
            ldc "."
            aastore
         4: .line 620
            invokestatic freemarker.core._MessageUtil.newMethodArgInvalidValueException:(Ljava/lang/String;I[Ljava/lang/Object;)Lfreemarker/template/TemplateModelException;
            areturn
        end local 3 // int len
        end local 2 // int idx
        end local 1 // int argIdx
        end local 0 // freemarker.core.BuiltInsForStringsBasic$substringBI$1 this
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    5     0    this  Lfreemarker/core/BuiltInsForStringsBasic$substringBI$1;
            0    5     1  argIdx  I
            0    5     2     idx  I
            0    5     3     len  I
    Exceptions:
      throws freemarker.template.TemplateModelException
    MethodParameters:
        Name  Flags
      argIdx  
      idx     
      len     final

  private freemarker.template.TemplateModelException newIndexLessThan0Exception(int, int);
    descriptor: (II)Lfreemarker/template/TemplateModelException;
    flags: (0x0002) ACC_PRIVATE
    Code:
      stack=6, locals=3, args_size=3
        start local 0 // freemarker.core.BuiltInsForStringsBasic$substringBI$1 this
        start local 1 // int argIdx
        start local 2 // int idx
         0: .line 630
            new java.lang.StringBuilder
            dup
            ldc "?"
            invokespecial java.lang.StringBuilder.<init>:(Ljava/lang/String;)V
            aload 0 /* this */
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI$1.this$1:Lfreemarker/core/BuiltInsForStringsBasic$substringBI;
            getfield freemarker.core.BuiltInsForStringsBasic$substringBI.key:Ljava/lang/String;
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
            invokevirtual java.lang.StringBuilder.toString:()Ljava/lang/String;
            iload 1 /* argIdx */
            iconst_3
            anewarray java.lang.Object
            dup
            iconst_0
         1: .line 631
            ldc "The index must be at least 0, but was "
            aastore
            dup
            iconst_1
            iload 2 /* idx */
            invokestatic java.lang.Integer.valueOf:(I)Ljava/lang/Integer;
            aastore
            dup
            iconst_2
            ldc "."
            aastore
         2: .line 629
            invokestatic freemarker.core._MessageUtil.newMethodArgInvalidValueException:(Ljava/lang/String;I[Ljava/lang/Object;)Lfreemarker/template/TemplateModelException;
            areturn
        end local 2 // int idx
        end local 1 // int argIdx
        end local 0 // freemarker.core.BuiltInsForStringsBasic$substringBI$1 this
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    3     0    this  Lfreemarker/core/BuiltInsForStringsBasic$substringBI$1;
            0    3     1  argIdx  I
            0    3     2     idx  I
    Exceptions:
      throws freemarker.template.TemplateModelException
    MethodParameters:
        Name  Flags
      argIdx  
      idx     
}
SourceFile: "BuiltInsForStringsBasic.java"
EnclosingMethod: freemarker.core.BuiltInsForStringsBasic$substringBI.calculateResult:(Ljava/lang/String;Lfreemarker/core/Environment;)Lfreemarker/template/TemplateModel;
NestHost: freemarker.core.BuiltInsForStringsBasic
InnerClasses:
  substringBI = freemarker.core.BuiltInsForStringsBasic$substringBI of freemarker.core.BuiltInsForStringsBasic
  freemarker.core.BuiltInsForStringsBasic$substringBI$1