| Parameter | Description |
|---|---|
| fs | A string to modify. |
| index | A reference to an index in bytes (not characters). Incremented by 1 to 4 depending upon the UTF-8 encoded size of the character written. |
| rune | A rune to write to the string, encoded as UTF-8. |
FormatError FormatError.None if successful. Returns FormatError.Overflow if the index is invalid or if there is not enough space to store the encoded rune.
Writes a Unicode.Rune at an index of this string. Increments the index to the position of the next character.