code: function(string) {
  		var index = this.stringLookupQuick[string];
  		// If missing, allocate now
  		if (index === undefined) {
  			index = this.stringLookup.length;
  			this.stringLookup.push( string );
  			this.stringLookupQuick[string]= index;
  		}
  		return index;
  	}
docs: Allocate new ID to return the ID of an existring
  string from file string lookup table.