remainderUntilIndex
Returns the remainder of the parsing result, truncated to the specified index relative to the original source text.
For example, if the source is "Hello, world!" and the parsing completes with "Hello", the regular remainder would be ", world!". If this function is called with an index of 10, it will return ", wor".
Return
the substring from the start of the remainder to the specified index
Parameters
index
the index to which the remainder should be returned