what is %prec in yacc code example

Example: what is %prec in yacc

%prec is short of precedense which is sufficient to allow yacc to resolve the 
parsing conflicts in accordance.
Suppose, 

notype_declarator:
      notype_declarator '(' parmlist_or_identifiers  %prec '.'

is used which declares that the construct has the same precedence as the '.' 
operator, which have been specified earlier.