Checks if the character at the given position is a valid HTML tag start.
| chunk |
The text chunk to examine |
| chunk_pos |
The position in the chunk to check (should be after '<') |
| is_end_of_chunks |
If true, format markers at the end are treated as definitive |
|
1: Valid HTML tag start, 0: Not valid HTML, -1: Cannot determine (need more characters) |