Invisible XML, ixml for short [ixml], is a notation and process that uses context-free grammars to describe the format of textual documents, allowing documents to be parsed into an abstract parse-tree, which can be processed in various ways, but principally serialised into an XML document, thus making the implicit structure of the textual document explicit in the XML.
While most current ixml grammars are small (the grammar for ixml itself for example is around 70 lines), it can be envisaged that in the future large grammars will emerge containing subparts that are authored by different people. As an example, there is an ixml grammar for XPath 4 at around 350 lines [jwl] which could be used by grammars for languages that use XPath 4.
In [vdb], van den Brand et al. note the advantage of context-free generalised parsing, which is used by ixml, over other restricted forms:
"the class of context-free grammars is closed under union, in contrast with all proper subclasses of context-free grammars. [...] The compositionality of context-free grammars opens up the possibility of developing modular syntax definition formalisms. Modularity in programming languages and other formalisms is one of the key beneficial software engineering concepts."
What this is saying, is that if you have, for instance, two LL1 grammars and merge them, the result may not still be LL1, but if you merge two general context-free grammars, the result will still be context-free, and this is one of the advantages of context-free generalised parsing, that you can modularise them.