_replaceAndContinue = function(block, replace_block, match_name) {
                        replacement = _replaceAtPosition(_indexOfGroup(match, group_keys[i]), block, match_name ? _wrapCodeInSpan(match_name, replace_block) : replace_block, replacement);
                        processNextGroup();
                    }
takes the code block matched at this group, replaces it
with the highlighted block, and optionally wraps it with
a span with a name

@param {string} block
@param {string} replace_block
@param {string|null} match_name