Double escaping?

[exside]

Not sure if this makes sense when having the escape spec in mind (you know that way better!), but what if a character is already escaped within the string to escape? The current code will double escape escaped stuff, I'm using a custom version that doesn't do that, e.g. changed to this:

// If the character is not handled by one of the above rules and is
// greater than or equal to U+0080, is `-` (U+002D) or `\` (U+005C) or 
// `_` (U+005F), or is preceded by a `\` (escape) already,
// or is in one of the ranges [0-9] (U+0030 to U+0039), [A-Z] (U+0041 to
// U+005A), or [a-z] (U+0061 to U+007A), […]
if (
	codeUnit >= 0x0080 ||
	codeUnit == 0x002D ||
	codeUnit == 0x005C || // custom: no double escapes!
	codeUnit == 0x005F ||
	string.charCodeAt(index-1) == 0x005C || // custom: no double escapes!
	codeUnit >= 0x0030 && codeUnit <= 0x0039 ||
	codeUnit >= 0x0041 && codeUnit <= 0x005A ||
	codeUnit >= 0x0061 && codeUnit <= 0x007A
) {
	// the character itself
	result += string.charAt(index);
	continue;
}

if this makes any sense for this project I'm glad to open a PR with the change, but I can imagine it is either against the spec, the purpose of this module or will break backward compatibility and can therefore not be done...