anchor.diff:      : '//' ~[\r\n]* '\r'? '\n' -> channel(HIDDEN)
       ;
   
  +//\u000C : change page
   WS  :   [ \r\t\u000C\n]+ -> channel(HIDDEN)
       ;
positive.code: 
  
  guard
      : 'EMPTY'
      | signal
      | expr
      | 'timeout' '(' expr ')'
      | guard '<and>' guard
  
negative.code: atom
      :  'skip'
      |  ID '=' expr
      |  '!' signal                   // !s (single or multi-sending), !s[0], !s[1][1]
      |  'suspend' '(' time=expr ')'
      ;
  
  