* which could indicate an opening token. Returns the number of "vague" chars.
* The last continuous sequence of whitespace, optionally followed by a "<" is
* treated as "vague" because whitespace may be discarded if the upcoming opening
* which could indicate an opening token. Returns the number of "vague" chars.
* The last continuous sequence of whitespace, optionally followed by a "<" is
* treated as "vague" because whitespace may be discarded if the upcoming opening