[xslt30] Visibility of xsl:param

[michaelhkay]

The XSLT 3.0 spec makes confusingly inconsistent statements about the visibility of global parameters.

The grammar for xsl:param does not allow a visibility attribute.

In §3.5.3.1, under xsl:expose, we say "The visibility of a variable declared using an xsl:param element is always public."

§9.6 (Static parameters) says: "When the static attribute [of xsl:param] is present with the value yes, the visibility attribute must not have a value other than private." But in fact, no visibility attribute is allowed by the grammar. It is clear in this section that the intent is for static parameters to always be private: there is a note explaining why (specifically, so they cannot be overridden, which is necessary to allow separate compilation of packages); however, I don't see why visibility="final" can't be allowed, which would achieve the same aim.

I think one aspect of this that the spec fails to address is: when package P "uses" package Q, it is presumably using a version of Q whose static parameters have been bound to particular values. But there is no way for P to say what these values should be. There can be two compiled instances of Q with different values bound to the static parameters, and the effect of using these two instances is likely to be quite different.