Re: [Xsltforms-support] XSLTForms enhancements?

[Mats E. <mat...@li...>]

Hi Alain, Just for background, many of these enhancements were necessary to make it possible to run XSLTForms as offline forms (compare InfoPath).
- Some deeper changes were required to make XSLTForms work in Chrome App context. Google Chrome imposes some unfortunate restrictions on browser apps, including 1) banning synchronous XMLHttpRequests and 2) forbidding inline scripts. To cope with the former, XSLTForms' init functions had to be rewritten as async functions with continuation callbacks, and for the latter, xsltforms.xsl had to be extended with an option to output scripts into separate resource files (I am using an XSLT 2.0 stylesheet that includes xsltforms.xsl), which in turn required some changes to XSLTForms' subform loading scripts for example. Maybe such extensive changes are not required for apps in other browsers, however, Chrome still offers significant advantages (speed, app deployment options, ...) which justified these efforts. File access, as well as local storage access, required extending the submission module to interface with the chrome.fileSystem and chrome.storage.local APIs.
- I implemented a separate transform() function in the saxon namespace, however I agree that the solution you propose would be much more elegant. The trickiest thing with including the SaxonCE library was to tweak it such that it loads synchronously as a normal js library! Having access to XSLT 2.0 can be quite useful in offline forms where one cannot call upon a server to do transformations, schematron validation etc.!
- True, in Web Worker context there is no access to the page document object. A few deeper changes were required to XSLTForms code to allow fairly arbitrary XPath expressions to be evaluated in Web Worker context. Some of the XPath function implementations in XSLTForms depend on the page document object which is not available in Web Worker context and also not sensible to serialize. I solved it by making sure functions access all their resources via the XPath evaluation context object (which had to be extended with a reference to the XForms model object), and serialized to a proper depth. 
- For XML schema validation, I am calling the following library: https://github.com/hubgit/xml.js/tree/dtd-validation. I think it works in all browsers!
- Both validation functions are currently XPath extension functions (maybe they could be implemented as extension actions instead -- or as emulated web-service operations accessible via the submission element so as to keep things standard?). I use them in my offline forms to validate instance documents opened by the user from the file system, or for validating form entries with an approach similar to this: http://wiki.orbeon.com/forms/how-to/logic/external-validation, not requiring calling an external service. I have them evaluated in a non-blocking background thread using the @async='true' extension.
- parse-xml() (which by the way seems to be a standard function in a more recent version of XPath) replaces xf:setnode in the following way: 
<xf:insert nodeset="instance('data')" origin="parse-xml(transform(...))"/> (for example)
- Another often needed improvement I've implemented is the xf:select1/@selection="open" (i.e. combobox). It's a simple change that leverages the HTML 5 @datalist.
I will think how to best share these extensions! Whatever makes it easier to potentially have some of these make it into the official version! :)
Kind regards,Mats 
On Sun, 10 Apr 2016 21:45:52 +0200 ala...@ag... wrote:

  
    
  
  
    Hi Mats,
- Allowing XSLTForms to be run as Chrome Apps, with
                  file save/open functionality etc.
    Could you please write some documentation about how you succeeded?
    It might be added in XSLTForms Wikibook, for example.- Embedding SaxonCE library so that transform()
                  function can run XSLT2 transforms
    Have you modified the transform() function so that it is looking at
    the version of the stylesheet? Could this better be considered as a
    global option to be added in config files?- Adding @async attribute to xf:setvalue/xf:insert
                  elements for non-blocking evaluation of long running
                  XPath expressions in Web Workers
    Web Workers are not available in old browsers but all recent ones do
    now! I did not try to use them yet (priorities...) and I still
    wonder how they can access the XML DOM in the main page: is it a
    problem??- Adding validate-with-xml-schema() function, using
                  xmllint library
    Is it that Chrome Apps allow you to link C libraries?- Adding validate-with-schematron() function, using
                  SaxonCE. Useful for doing more advanced form
                  validations using SVRL.
    Is it an XPath function? When are you calling it? Before submission?
    XForms is based on validation at node level whenever a value has
    been modified: do you think that it is also compatible with SVRL?- Adding parse-xml() function, believe replacing
                  need for xf:setnode
    xf:setvalue is there to set a value not to import nodes... That's
    why I added xf:setnode with the serialized XML string as parameter.
    In what context do you use parse-xml()? Which document/instance owns
    the resulting nodes?
Would be glad to contribute these as well as some
                  other extensions and performance optimizations.

    Will be glad to look at them in details!! Is it your intent to
    publish source files independently or to fork the repository?

    Thanks!

    Alain