nl_tokens: return a predicate which matches files with the given extension ( s ) ;
pl_tokens: function filenameExtensionFilter ( ext ) { if ( typeof ext === 'string' ) { return ( _ , path ) => path . endsWith ( '.' + ext ) ; } else if ( ext instanceof Array ) { return ext . <mask> ( filenameExtensionFilter ) . reduce ( pcomp ) ; } }