Support xsl:use-package with xsl:package-location

[Arithmeticus]

Unless I am misreading the specs (which I do commonly enough), there is currently no way for an XSLT writer using xsl:use-package to indicate where the package is to be found, except outside the XSLT environment. I propose to allow xsl:use-package to contain zero or more xsl:package-location children. I propose the addition of an element and not an attribute, because a package may be in multiple locations, and need nuance, as noted below.

Attributes:

• @href, on the model of xsl:import and xsl:include, would specify by relative or absolute URI where the package is.
• @priority (default 0) would provide a mechanism to indicate whether the specified xsl:package-location should override (value greater than 0), or simply provide a fallback for (less than or equal to 0), the preconfigured place the package should be retrieved from.
• @use-when would allow a developer to manage different versions of a package for different cases.

Other attributes given to xsl:package-location would need discussion.

[michaelhkay]

This came up again on StackOverflow.

I think the idea of a set of xsl:package-location children giving alternative locations is sound. There could be an @Format attribute, with values for example

source - URI location of the top-level module of the package in source XSLT form
zip-source - URI of a ZIP archive holding all the modules of the package in source form
saxon:sef - URI location of a compiled package in Saxon SEF format

[sashafirsov]

The browser uses the import map for similar purpose. It is defined outside of XSLT template as transformation engine property. custom-element uses this mecanism for defining the templates via module name aliasing. It also allows to use bundle mechanizm which is similar to zip archive( online the zip encoding applied by the server and bundling by XML+IDs).

The import map mechanizm is self-trigerred by transformation engine when URL is a module name( i.e. starts with alphanumerical ID and does not have protocol/port prefix). When the https://, or relative path like ../ are used, the module resolution is done relatively to the current template location.

That said, the use of xsl:use-package with existing module resolution does not bring much. Instead, making the import map an officially supported protocol would be unvaluable.

[michaelhkay]

Fixed by PR #1888