Here is a list of settings that exist in JavaCC 21 but are not (and never were) present in the legacy JavaCC tool:

• BASE_NAME This option is used to set the name of the parser, lexer, constants, and NFA data files instead of using the default naming convention that prefixes these files with the name of the grammar file. If this option is set to an empty string (BASE_NAME=“”;) then these filenames will not receive a prefix. See the PARSER_CLASS, LEXER_CLASS, and CONSTANTS_CLASS settings to individually specify the names for these classes.
• BASE_NODE_CLASS When defined, this option allows you to specify the name of the base node from BaseNode to a name that you prefer, such as SimpleNode. This class implements the Node interface and is extended by the production classes generated by JavaCC.
• BASE_SRC_DIR This supersedes the older OUTPUT_DIRECTORY setting. Files are generated relative to the BASE_SRC_DIR, i.e. taking into account the package naming. If this is unset, BASE_SRC_DIR is assumed to be the directory where the grammar is.
• CONSTANTS_CLASS This option is used to set the name of the generated constants file instead of using the default file name based on the grammar filename.
• DEACTIVATE_TOKENS This setting allows you to indicate that certain token types are de-activated by default when you instantiate the parser. Something like: DEACTIVATE_TOKENS=OPEN_PAREN,CLOSE_PAREN; would mean that those two tokens are not active by default when you instantiate the parser. Of course, you could use ACTIVE_TOKENS(….) to activate them when needed in the parse.
• DEFAULT_LEXICAL_STATE This option allows you to specify the default lexical state for a grammar instead of relying on the legacy value of DEFAULT. Setting a meaningful DEFAULT_LEXICAL_STATE is extremely desirable for grammars that may be INCLUDEd by other grammars because it will prevent accidental duplication of lexical productions.
• ENSURE_FINAL_EOL With this setting turned on (it is off by default) the generated parser ensures that the input file ends with a newline character. (It tacks one on if it is not present.) This is a nitpicking detail but it is surprisingly difficult to write certain grammars (ones that are very line-oriented) if you cannot be sure that every line (including the last one!) ends with a newline.
• EXTRA_TOKENS This setting allows you to indicate some additional token types that are not defined with regular expressions in the lexical grammar. This can be useful particularly in token hook routines.
• FAULT_TOLERANT This turns on the experimental support for building a fault tolerant parser. It is off by default.
• FREEMARKER_NODES Defining this option inserts extra code into Node objects that implement FreeMarker (template) API's. This allows you to use FreeMarker templates to walk the node tree using a more natural syntax.
• LEXER_CLASS This option sets the name of the generated lexer file instead of using the default file name based on the grammar filename. This option also sets the name of the NFA data file to use this same prefix. For example, LEXER_CLASS=“FooLexer”; generates FooLexer.java and FooNfaData.java.
• MINIMAL_TOKEN Default is not set (false) Token Chaining is supported by adding two fields to Tokens. If token chaining is _not_ required, define this option to skip adding these two additional fields.
• PARSER_CLASS This option is used to set the name of the generated parser file instead of using the default file name based on the grammar filename.
• PARSER_PACKAGE By default, all classes are generated with no package (default package). When this option is defined, all generated classes will have the specified package inserted at the top of the files. This option improves the organization of source code in large non-trivial projects.
• PRESERVE_LINE_ENDINGS This is now off by default. That means that all Windows/DOS style line endings (\r\n) are converted to UNIX/MacOS style (\n) internally when the file is read in. Note, by the way, that one advantage of this and the TABS_TO_SPACES option is that if you convert tabs to spaces and line endings to \n then your grammar's lexical specification can be a bit simpler. And your own code that runs over Tokens and Nodes. Your code can just assume that any line endings are a simple \n and and your horizontal whitespace is just spaces, not a mix of tabs and spaces, independently of what platform the generated code is running on.
• SMART_NODE_CREATION This is the default behavior, so you would have to explicitly turn it off. It means that if no JJTree-style tree-building annotation is used, then a new Node will be created if there are more than one Nodes on the stack. So, a production like A (B)* will create a new Node if there are one or more B's after the A. If there is only an A then the production will just leave it on the stack. It is our belief that this is the behavior that most people would want most of the time.
• SPECIAL_TOKENS_ARE_NODES This sets whether to add so-called “special tokens” to the AST. By default, it is set to false. (Note that this option and TOKENS_ARE_NODES are meaningless if TREE_BUILDING_ENABLED is set to false.)
• TABS_TO_SPACES This is an integer (typically from 1 to 8, in practice) that defines how many spaces a tab stop is. This is now set to 8 by default. (Until very recently, the default was that the option was off.) This means that all TAB characters (\t) are converted to spaces when the file is read in. Note that, if you turn this off, all reported error locations simply treat a tab character as one horizontal offset. If you want JavaCC to report errors as if a TAB stop is 4 spaces, say, you need to set TAB_SPACES=4 in your settings.
• TOKENS_ARE_NODES This sets whether we add Tokens as terminal nodes to the AST. By default, it is true.
• TREE_BUILDING_DEFAULT Default is true. A parser generated by JavaCC 21 automatically includes the code to build an AST (Abstract Syntax Tree). When set to false, the code is still available in the generated code but the AST is not built until you turn it on in the code.
• TREE_BUILDING_ENABLED Default is true. A parser generated by JavaCC 21 automatically builds a tree. If you don't want a tree or want to build a tree in your own code actions, set TREE_BUILDING_ENABLED=false; and no tree building code is inserted into your parser.
• USE_PREPROCESSOR When defined, JavaCC 21 will process preprocessor statements. The statements conform the behavior of Microsoft's C# #define/#undef and #if/#elif/#else/#endif constructs that are used to conditionally turn on and off ranges of lines in the grammar file.

See deprecated settings for a list of legacy JavaCC options that no longer exist in JavaCC 21.