text: #ifndef SASS_AST_FWD_DECL_H
  #define SASS_AST_FWD_DECL_H
  
  /////////////////////////////////////////////
  // Forward declarations for the AST visitors.
  /////////////////////////////////////////////
  namespace Sass {
  
    enum Output_Style { NESTED, EXPANDED, COMPACT, COMPRESSED, FORMATTED };
  
    class AST_Node;
    // statements
    class Statement;
    class Block;
    class Ruleset;
    class Propset;
    class Bubble;
    class Media_Block;
    class Feature_Block;
    class At_Rule;
    class Keyframe_Rule;
    class At_Root_Block;
    class Declaration;
    class Assignment;
    class Import;
    class Import_Stub;
    class Warning;
    class Error;
    class Debug;
    class Comment;
    class If;
    class For;
    class Each;
    class While;
    class Return;
    class Content;
    class Extension;
    class Definition;
    class Mixin_Call;
    // expressions
    class Expression;
    class List;
    class Map;
    class Binary_Expression;
    class Unary_Expression;
    class Function_Call;
    class Function_Call_Schema;
    class Variable;
    class Textual;
    class Number;
    class Color;
    class Boolean;
    class String_Schema;
    class String;
    class String_Constant;
    class String_Quoted;
    class Media_Query;
    class Media_Query_Expression;
    class Feature_Query;
    class Feature_Query_Condition;
    class At_Root_Expression;
    class Null;
    class Parent_Selector;
    // parameters and arguments
    class Parameter;
    class Parameters;
    class Argument;
    class Arguments;
    // selectors
    class Selector;
    class Selector_Schema;
    class Selector_Reference;
    class Selector_Placeholder;
    class Type_Selector;
    class Selector_Qualifier;
    class Attribute_Selector;
    class Pseudo_Selector;
    class Wrapped_Selector;
    class Compound_Selector;
    class Complex_Selector;
    class Selector_List;
  
  }
  
  #endif
  