LuaExpat is a SAX XML parser based on the Expat library. SAX is the Simple API
for XML and allows programs to:
- process a XML document incrementally, thus being able to handle huge documents
  without memory penalties;
- register handler functions which are called by the parser during the
  processing of the document, handling the document elements or text.

With an event-based API like SAX the XML document can be fed to the parser in
chunks, and the parsing begins as soon as the parser receives the first document
chunk. LuaExpat reports parsing events (such as the start and end of elements)
directly to the application through callbacks. The parsing of huge documents can
benefit from this piecemeal operation.

See also: https://github.com/lunarmodules/luaexpat