Operator Scope of Action:
Operator First Added:
In addition, where may be argument that designates a particular (single) note other than this.
condition is a valid conditional test, i.e. it equates to true when matched.
value can be any expression, but is typically an attribute value. It can also be the number 1, i.e. if the test is true from that item then add one to the count.
sums the number of children of the current note whose prototype is 'p_Prototype'. If tested value is a string with spaces, e.g. "p Prototype" vs. "p_Prototype" then use double quotes around the value.