nl_tokens: Merge two visitors .
pl_tokens: function merge ( x , y ) { for ( const key of Object . keys ( y ) ) { if ( typeof x [ key ] === "function" ) { if ( x [ key ] . _handlers == null ) { const fs = [ x [ key ] , y [ <mask> ] ] x [ key ] = dispatch . bind ( null , fs ) x [ key ] . _handlers = fs } else { x [ key ] . _handlers . push ( y [ key ] ) } } else { x [ key ] = y [ key ] } } return x }