Figure 4-1 presents both syntaxes side by side. There are two things you'll immediately notice. The compact syntax is much more, well, compact. The XML syntax is, just as you'd expect, XML. It works well with generic XML tools (here a web browser), while the compact syntax isn't XML and must be used with other tools (here the text editor vim with a plug-in that highlights RELAX NG's compact syntax).

Figure 4-1. Comparing the RELAX NG XML syntax with its smaller compact syntax counterpart

These two statements summarize why both syntaxes are needed. The compact syntax is nice to work with, and you'll probably find it more pleasant to use to edit your schemas and to document your vocabularies. On the other hand, the XML syntax is wonderful if you want to generate RELAX NG schemas, as in Chapter 14 or to generate anything out of your RELAX NG schemas using the XML tools covered in Chapter 13. The ability to translate from one syntax to the other without information loss guarantees that you can use either while having access to both.