Check for processing instruction nodes.
The following construct(s) refer to this construct:
A ProcessingInstructionTest is one of a number of node tests
that are used in a step expression. The expression
processing-instruction() is true for any processing instructions.
You can also specify a string literal that must be equal to the value of the
target application for the test to succeed.
Select all processing instructions in the current collection:
input()//processing-instruction()
Select all processing instructions that use the target application "xm-replace_text":
input()//processing-instruction("xm-replace_text")