docs: function( json, params, callback ){
      var where = sql.parse( 'select * from foo where '+ params.where).where;
  
      var features = [];
      _.each(json.features, function(f){
        var props = f.attributes || f.properties;
        var param = where.conditions.left.value;
        var val = where.conditions.right.value;
        if ( ( this.whereOps[ where.conditions.operation ] && props[ param ] && this.whereOps[ where.conditions.operation ]( props[ param ], val ) ) || param == val ) {
          features.push( f );
        }
      }, this);
      json.features = features;
  
      delete params.where;
      // recycle the data + params through the filter fn
      this.filter( json, params, callback );
    }