@verb #62:"_name" this none this rxdo #60
@program #62:"_name" this none this
":_name(string) => full option name corresponding to string "
"               => $failed_match or $ambiguous_match as appropriate."
if ((string = args[1]) in this.names || string in this.extras)
  return string
endif
char = (namestr = this._namelist)[1]
if (!(i = index(namestr, char + string)))
  return $failed_match
elseif (i != rindex(namestr, char + string))
  return $ambiguous_match
else
  j = index(namestr[i + 1..length(namestr)], char)
  return namestr[i + 1..i + j - 1]
endif
.