Function parse_number_or_angle 

fn parse_number_or_angle<'i, 't>(
    context: &ParserContext<'_>,
    input: &mut Parser<'i, 't>,
    allow_none: bool,
    allowed_channel_keywords: ChannelKeyword,
) -> Result<ColorComponent<NumberOrAngleComponent>, ParseError<'i>>

Parse an <number> or <angle> value.