RE: Back to Basics: XPath and Context Node

[Kay Michael <Michael.Kay@xxxxxxx>]

> sect 1: . . . "Several kinds of expressions change the 
> context node; only
> predicates change the context position and context size." 
> 
> 	Q: by implication, then, predicates do not change the context
> 		node?

No, it doesn't say that and it doesn't mean that.
> 
> Sect. 2: "child::para selects the para element children of the context
> 	node."
> 
> 	Q: so, if I have this xsl
> 
> 		< . . . .std. header stuff and PI . . .>
> 		<xsl:template match="/">
> 			<xsl:apply-templates />
> 		<xsl:template>
> 
> 		<xsl:template match="child::para or child::*">
> 			---some stuff ---
> 		</xsl:template>

You can't say this because you can't use "or" in a pattern. Perhaps you mean
"|".
> 	
> 	The context node for my child:: matches is the root 
> "/", yes? 

No, the rules for pattern matching are that a match is attempted with each
ancestor of the node being matched (plus the node itself). This is in XSLT
section 5.2, first para.

> 	my location path is essentially redundant b/c child::* includes 
> 	all para's anyway, obviating the "or," right?

Yes, if you read "or" as "|".
> 
> 
> Sect 2.1: Location steps: . . ."The final node set is the node-set
> 	selected by the location step"
> 
> 	Q: reading the BNF preceding this question, am I right that
> 	location steps only occur in RelativeLocationPaths (cf. [3]
> 	immediately before 2.1)? 

Steps are used directly only within a RelativeLocationPath but a
RelativeLocationPath forms part of many other constructs including an
AbsoluteLocationPath.

 And, then, is the location 
> step in this
> 	case <=> with the "location path" -- same thing as?

No, the path is a sequence of steps.
> 
> Sect 3.2 Function calls:  . . . "A FunctionCall expression is 
> evaluated by
> using the FunctionName to identify a function in the 
> expression evaluation
> context function libarary, evaluating each of the arguments, 
> converting
> each argument to the type required by the function, and 
> finally calling
> the funtion, passing it the converted arguments."
> 
> 	Q: Anyone courageous to unpack this-- particularly the 
> astounding
> 	concatenation: "the expression evaluation context function
> 	libarary"?  In the absence of an example here, it's not clear to
> 	me what exactly the "function call" is, unless --and I am 
> 	certainly wrong here but it's all I can think of in my
> 	non-programmer's mindset-- "xsl:call-template"?

A function call is something like number('23.4') or true() or
contains(.,'fred').

The "expression evaluation context function library" means the function
library associated with the context in which the expression is evaluated, a
concept explained in XPath section 1.
> 
> And finally, in due deference to nomenclature issues, 
> "xsl:call-template"
> or "xsl:variable" or xsl:choose -- these are properly called 
> XSL elements,
> xslt elements, xslt functions, xslt operators, xslt commands, xslt
> template types, xslt transformers ("more than meets the eye")

They are all XSL elements, in fact the ones you list are all XSL
instructions, which is a subtype of XSL elements. But not all XSL elements
are instructions, e.g. xsl:template isn't.
 
Mike Kay


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