code: function insert(name, base, once) {
  
        name = fullPath(name, base)
  
        // _files is an object with keys of all the processed files
        var f = _files[name] | 0
        if (f > 1) return false     // 2: already include_once
        if (once) {
          _files[name] = 2          // mark as include_once
          if (f) return false       // 1: already included
        }
        else
          _files[name] = 1          // mark as normal include
  
        // abort if the file is an ancestor (is in the queue)
        f = _queue.length
        while (--f >= 0) {
          if (_queue[f][0] === name) return false
        }
  
        _queue.push([base, data])
        readImport(name, ++_level)
  
        return true
      }
docs: Helpers ----- 
  Pushes the current filename and remaining data and inserts a new file.
  Skips the insertion if the file is in the queue, avoiding recursion,
  or if it's an include_once directive and the file was already inserted
  anywhere in the process.
  
  @param   {string}  name - The file's name being included, relative to base
  @param   {string}  base - The file's name being processed
  @param   {boolean} once - `true` for unique inclusion
  @returns {boolean} - `true` if the file can be inserted