lib/filter.js
function _arrayProperties (arr, mask) {
  var obj = _properties({_: arr}, {_: {
    type: 'array',
    properties: mask
  }})
  return obj && obj._
}
function _arrayProperties (arr, mask) {
  var obj = _properties({_: arr}, {_: {
    type: 'array',
    properties: mask
  }})
  return obj && obj._
}
function _arrayProperties ( arr , mask ) { var obj = _properties ( { _ : arr } , { _ : { type : 'array' , properties : mask } } ) return obj && obj . _ }
wrap array & mask in a temp object; extract results from temp at the end
wrap array & mask in a temp object ; extract results from temp at the end