A total, left-to-right scan of an XML source binary that produces the positions Saxy does not.

Saxy 1.6.1 passes handlers no position data of any kind and has no option to enable it (deps/saxy/lib/saxy/handler.ex), so positions are produced by this independent scan and zipped against the SAX event stream by index in Statifier.Parser.Handler - the Nth start-tag record this scanner finds is the Nth :start_element Saxy emits.

The scan only ever answers "is this a markup construct, and where does it start and end". It classifies each < by the bytes that follow it - <!-- comment (skipped to -->), <![CDATA[ (skipped to ]]>), <!DOCTYPE (skipped to >, honoring an internal [...] subset), <? PI or the XML declaration (skipped to ?>), </ an end tag, anything else a start tag - and never interprets content, expands entities, or validates. A self-closing <b/> emits two records, a :start and an :end with identical spans, so the record stream stays 1:1 with Saxy's element events by construction.

It is a total function: it never raises, on any binary, including malformed or truncated XML. On a malformed document, Saxy's own error is what surfaces to Statifier.Parser.parse/1; this scanner's only obligation on such input is to return a list without crashing, since a well-formed document is Saxy's job to reject, not this scanner's.