Basic XSLT is not well suited to stream based processing, and STX fills this niche.
In contrast, SAX streams XML events such as "open element," "close element," and "text node" so that other software can begin interpreting information immediately, before the end of the file is reached.
Unfortunately some software can't effectively use XML fragments this way and must build up the whole document to begin processing.
As it can discard nodes immediately after processing, memory use is significantly lower than that of XSLT.
Unlike STX which is declared using an XML syntax, these two projects associate SAX events with callback functions: