Analyzed Layout and Text Object
Analyzed Layout and Text Object (ALTO) is an open XML schema originally developed by the EU-funded METAe project. ALTO files describe the placement, size, and style of text in an image of a digitized document, as well as other elements of the document's layout, such as margins, headings, columns, and illustrations.
Source: Wikipedia — Analyzed Layout and Text Object (CC BY-SA 4.0)