term     ::= ( text | expr | pipeline ) ','? ;

  pipeline ::= container?  trail+ ;

  trail    ::= var | '[' term ']' ;

  container::= '[' term* ']'
             |  '{' ( dot_name (':' text | '=' term )
                    | other+ ','?
                    )* '}' ;

  var      ::= (':'+ | '.'+) name ( '(' term* ')' )? ;
  name     ::= \w+ ;
  dot_name ::= [\w\.]+ ;

  expr     ::= '=' text ;
  text     ::= word ( group word? )* ; -- group で始まるのは、container.

  group    ::= [\(\[\{] ( text | ',' )* [\}\]\)]

  word     ::= [\w\$\-\+\*/%<>] other* ;
  other    ::= [\w\$\-\+\*/%<>:\.!=] ;