function checkForAcceptableEscape(char, charSource) {
	if (!charSource.startsWith("\\")) {
		return false;
	}
	const match = /(?<=^\\+).$/su.exec(charSource);

	return match?.[0] !== String.fromCodePoint(char.value);
}
Checks whether a specified regexpp character is represented as an acceptable escape sequence.
This function requires the source text of the character to be known.
@param {Character} char Character to check.
@param {string} charSource Source text of the character to check.
@returns {boolean} Whether the specified regexpp character is represented as an acceptable escape sequence.