One attribute of an element, carrying two spans rather than one.

location covers the whole name="value" text, quotes included - the span a diagnostic underlines when the attribute itself is the problem. value_location covers only the text inside the quotes, and exists for ADR-0014: an expression span is relative to the expression string, and value_location is the anchor Statifier.Parser.Location.resolve_span/4 composes it against to produce a document position.

The attribute's name begins at location.start_line / location.start_column exactly, so no separate name span is stored.

value is the XML 1.0 3.3.3-normalized, entity-expanded text while value_location covers raw source (ADR-0043). A literal TAB/LF/CR in the raw text becomes a space in value; a character reference such as 
 keeps its decoded character verbatim - that contrast is 3.3.3's whole point, and it is drawn by walking the raw slice against Saxy's expanded value rather than by inspecting value alone, since a literal and an expanded 
 are indistinguishable characters once expanded. value_location's raw text can therefore differ from value in both length and content, so an offset inside the value does not map 1:1 onto the source. resolve_span/4 accounts for the difference by walking the raw slice against the normalized value; Location.slice(value_location, source) recovers the raw text on demand, so nothing needs to be stored here.