
At first sight, processing instruction is at odds with the XML concept that
processing is always derived from the structure. As we saw in the first
chapter, with SGML and XML, processing is derived from the structure of
the document. There should be no need to insert specific instructions in a
document. This is one of the major improvements of SGML when compared
to earlier markup languages.
That’s the theory. In practice, there are cases where it is easier to insert
processing instructions rather than define complex structure. Processing
instructions are a concession to reality from the XML standard developers.
You already are familiar with processing ...