nl_tokens: Check if capabilities are available or throw an error .
pl_tokens: function featureCheck ( globalScope , features ) { var i , j , k , l , feature , path for ( i = 0 , j = features . length ; i < j ; i ++ ) { path = features [ i ] if ( typeof path [ 0 ] === 'string' ) { feature = globalScope for ( k = 0 , l = path . length ; k < l ; k ++ ) { if ( ! ( path [ k ] in feature ) ) throw new Error ( 'Missing ' + path . slice ( 0 , k + 1 ) . join ( '.' ) + ' feature which is required.' ) feature = feature [ path [ k ] ] } } else { feature = path [ 0 ] for ( k = 1 , l = path . length ; k < l ; k ++ ) { if ( k > 1 ) feature = feature [ path [ k ] ] if ( typeof feature === 'undefined' ) throw new Error ( 'Missing ' + <mask> [ 0 ] . name + path . slice ( 1 , k + 1 ) . join ( '.' ) + ' feature which is required.' ) } } } }