code: function (parameters, prefix) {
                  var
                      len,
                      idx,
                      parameter;
                  if (undefined === prefix) {
                      prefix = 0;
                  }
                  len = parameters.length;
                  if ("number" === typeof prefix) {
                      idx = prefix;
                      prefix = "";
                  } else {
                      idx = 0;
                  }
                  for (; idx < len; ++idx) {
                      parameter = parameters[idx];
                      if (parameter._prefix === prefix) {
                          return parameter;
                      }
                  }
                  return null;
              }
docs: Helper used to manipulate the list of parameters: retrieve one
  using prefix. If no prefix is specified or a number is used, get
  the first parameter with no prefix (starting at N if a number was
  used).
  
  @param {gpf.Parameter[]} parameters
  @param {String|Number} [prefix=0] prefix