RegExp constructor and oddly escaped new line characters

I have questions
1

This is a corner case when constructing RegExps from strings, line terminator characters preceded by a backslash appear to have a distinct behavior that I couldn't see reflected in the spec:

console.log([
  new RegExp('\n').source === new RegExp('\\\n').source,
  // true
  new RegExp('\t').source === new RegExp('\\\t').source,
  // false
], [
  new RegExp('\x0a').source === new RegExp('\\\x0a').source,
  // true
  new RegExp('\x03').source === new RegExp('\\\x03').source,
  // false
], [
  new RegExp('\u2028').source === new RegExp('\\\u2028').source,
  // true
  new RegExp('\u2018').source === new RegExp('\\\u2018').source,
  // false
])

live here

Is it a browser quirk or a spec bug? The three-backslash variants are rejected when the 'u' flag is used.

2

The .source accessor calls EscapeRegExpPattern, which says

The code points / or any LineTerminator occurring in the pattern shall be escaped in S as necessary to ensure that the string-concatenation of "/", S, "/", and F can be parsed (in an appropriate lexical context) as a RegularExpressionLiteral that behaves identically to the constructed regular expression.

So this is the behavior required by spec.

3

Many thanks @bakkot, I did a search and missed it.