Expat is described as 'XML parser library written in C. It stream-oriented parser in which an application registers handlers for things the parser might find in the XML document (like start tags). As one of the first available open-source XML parsers, Expat has found a place in many' and is an app in the development category. There are three alternatives to Expat for Mac, Windows, Linux and BSD. The best Expat alternative is libxml2, which is both free and Open Source. Other great apps like Expat are pugixml and TinyXML-2.
libxml2 is a software library for parsing XML documents. It is also the basis for the libxslt library which processes XSLT-1.0 stylesheets.
libxml2 is the most popular Windows, Mac & Linux alternative to Expat.
libxml2 is the most popular Open Source & free alternative to Expat.
In brief, TinyXML-2 parses an XML document, and builds from that a Document Object Model (DOM) that can be read, modified, and saved.