I’m confused by this rule. On the one hand the spec says:
A link label begins with a left bracket (
[) and ends with the first right bracket (]) that is not backslash-escaped. Between these brackets there must be at least one character that is not a space, tab, or line ending. Unescaped square bracket characters are not allowed inside the opening and closing square brackets of link labels.
On the other hand it says:
The link text may contain balanced brackets, but not unbalanced ones, unless they are escaped:…
In the 1st case it seems unescaped brackets are forbidden. In the 2nd case only unbalanced brackets are forbidden.