> It uses invalid HTML, with attribute syntax including brackets and parentheses
Brackets and parens are valid in attribute names.
Section 13.1.2.3 of the HTML standard[0] states:
> Attribute names must consist of one or more characters other than controls, U+0020 SPACE, U+0022 ("), U+0027 ('), U+003E (>), U+002F (/), U+003D (=), and noncharacters.
Brackets and parens are valid in attribute names.
Section 13.1.2.3 of the HTML standard[0] states:
> Attribute names must consist of one or more characters other than controls, U+0020 SPACE, U+0022 ("), U+0027 ('), U+003E (>), U+002F (/), U+003D (=), and noncharacters.
[0] https://html.spec.whatwg.org/#attributes-2