Extracts a sub-string of this string.
- Parameters:
-
| first | the 0-based position of the first character to return. Negative values are treated as 0. |
| count | the number of characters to return. If negative then all characters up to the end of this string are returned. |
| useUTF8 | true: perform Mid against the UTF8 representation of this string. false (default): perform it against the Unicode representation. |
- Returns:
- The extracted sub-string