Editing Punycode (section)

===Separation of ASCII characters===
First, all [[ASCII]] characters in the string are copied from input to output, skipping over any other characters. For example, "bücher" is copied to "bcher". If any characters were copied, i.e. if there was at least one ASCII character in the input,<!-- This is correct according to RFC. If there are no ASCII characters then there is no leading dash! This is dealt with by the "xn--" prefix, described later, which is not part of Punycode.--> an ASCII hyphen is appended to the output (e.g., "bücher" → "bcher-", but "ü" → "").

Note that hyphens are themselves ASCII characters. Thus, they can be present in the input and, if so, they will be copied to the output. This causes no ambiguity: if the output contains hyphens, the one that got added is always the last one. It marks the end of the ASCII characters.