At 2011-12-03 21:20 +0800, [email protected] wrote:
Gentlemen, what a spiteful language xquery is, not allowing an empty
statement. I want to "comment out" a line,
<Document>
{doc("p.xml")//STYLES/*} <--- Let's comment out this line
<Document>
{(: doc("p.xml")//STYLES/* :)}
BaseX makes [XPST0003] Expecting valid expression after "{".
<Document>
<!-- {doc("p.xml")//STYLES/*} -->
Works but ends up in output.
It's all because {} for some reason needs to be filled with some junk.
OK, adding "" works:
<Document>
{""(: doc("p.xml")//STYLES/* :)}
In XPath syntax, the empty string is not a valid expression:
http://www.w3.org/TR/2007/REC-xpath20-20070123/#prod-xpath-XPath
Your use of curly braces has to be populated with an XPath
expression. An XPath expression is evaluated after comments have
been removed.
http://www.w3.org/TR/2007/REC-xpath20-20070123/#comments
"Comments are lexical constructs only, and do not affect expression
processing."
Thus you need *something* to prevent the contents of the curly braces
to be empty after removing comments.
I tell my students to use () rather than "". This is an explicit
lesson in the class because of the intuition that a comment is an
expression, when it isn't.
I hope this explanation helps.
. . . . . . . . . Ken
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