`<` is highlighted as error in quoted value

[aeschli]

From microsoft/vscode#160143

< is highlighted as an error.

Reading https://dev.w3.org/html5/spec-LC/syntax.html#attributes-0 I don't think < in a quoted attribute value is a problem:

Attribute values are a mixture of text and character references, except with the additional restriction that the text cannot contain an ambiguous ampersand.

Single-quoted attribute value syntax
The attribute name, ... followed by the attribute value, which, in addition to the requirements given above for attribute values, must not contain any literal U+0027 APOSTROPHE characters ('), and finally followed by a second single U+0027 APOSTROPHE character (').

Double-quoted attribute value syntax
The attribute name, ... followed by the attribute value, which, in addition to the requirements given above for attribute values, must not contain any literal U+0022 QUOTATION MARK characters ("), and finally followed by a second single U+0022 QUOTATION MARK character (").