I use languages engine for getting AST tree.

I have declaration :
EchoStatement = ("echo" | "print") EchoArguments ";";
EchoArguments = [ Expression ( "," Expression )* ] | ( "(" [ Expression ( "," Expression )* ] ")" )  ;

Expression node has usual "expression" structure ( its definition too long , I think there is no need in this ).

The problem is in possibility for valid expression value , f.e.:
expression could be "( 1 + 2 )".

So it seems for string 'echo ( 1+2 );'
engine cannot determine in this case expression "1+2" as most appropriate result 
because EchoArguments could also have "(" , ")".  
( So engine has two choices : incorrect EchoArguments "(" , expression="1" , "+",
expression="2", ")" and correct EchoArguments = expression = "( 1+2 )" ).

As result I get on stderr ( or stdout , I'm not sure exactly ) :
Too many choices! EchoArguments : <php_operator,'('> <php_whitespace,' '>:<php_operator,'('> <php_whitespace,' '> <php_n
umber,'1'> <php_operator,'+'> <php_number,'2'> <php_whitespace,' '> <php_operator,')'> <php_separator,';'> <php_whitespa
ce,'\n    '> .

Engine should prefer and choose CORRECT constructions against many cases with incorrect result constructions.