lib/level.js
function(block, mod) {
        return PATH.join.apply(null,
            [block,
            '_' + mod,
            block + '_' + mod]);
    }
function(block, mod) {
        return PATH.join.apply(null,
            [block,
            '_' + mod,
            block + '_' + mod]);
    }
function ( block , mod ) { return PATH . join . apply ( null , [ block , '_' + mod , block + '_' + mod ] ) ; }
Get relative path prefix for block modifier.

@param {String} block  Block name.
@param {String} mod  Modifier name.
@return {String}  Path prefix.
Get relative path prefix for block modifier .