Current SVN version of Delphi Web Script now supports the following directives (all new but include and filter):

• $I, $INCLUDE, $F, $FILTER: include specified file (which can be on disk or come through the virtual file system), the FILTER variants will include the file after filtering it.

  {$INCLUDE 'mysource.inc'}

• $DEFINE, $UNDEF: define and un-define a conditional.

  {$DEFINE SPECIAL_CODE}

• $IFDEF, $IFNDEF, $ELSE, $ENDIF: allow specifying conditionally compiled blocks.

  {$IFDEF SPECIAL_CODE}
  ...special code here...
  {$ELSE}
  ...not so special code here...
  {$ENDIF}

• $HINT, $WARNING, $ERROR, $FATAL: output a custom compiler hint, warning or error message.

  {$HINT 'That is not wise...'}
  {$WARNING 'You should NOT be doing that!'}
  {$ERROR 'Do not do that. Period.'}
  {$FATAL 'After that, I won''t even try to compile your code!'}

Conditionals are case-insensitive names, conditional blocks can be nested.
Default conditionals when compiling can be adjusted via a new property in the TdwsConfiguration.

edit: added $FATAL