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Extension Instructions for HTML Component Lib
Added by Anonymous almost 15 years ago
Legacy ID: #7950191
Legacy Poster: Matt (mraccola)
I work on an application that uses XSLT to render the HTML representation of the
user interface. We would like to build a component library for our framework, something
along the lines of the core Flex or JSF components. It seems that the way to do this
would be to write custom extension instructions,
[http://saxonica.com/documentation/extensibility/instructions.html][1]. I tried
prototyping a simple panel component that will generate a fancy DIV around arbitrary
HTML content. Sample markup would look like this: <custom:panel ...>
</custom:panel> I am running into multiple issues
especially when I try to process the child content. The sample SQL extension
instructions don't really have true children so they aren't sufficient for me to use as
a basis for architecting the solution. I tried Googling different search terms trying to
see if anyone had done this before and didn't really get many hits. Overall the
programming model doesn't appear to be designed for extension. It seems you would need
to know a great deal about the inner workings of Saxon to make progress. Here is the
latest error I am hitting on while trying to declare variables within the custom panel
tag. This will give you an idea of the types of issues I am running into. In order for
me to troubleshoot this I will have to go it and read through some Saxon code to figure
out what is going on. java.lang.AssertionError: Internal error: invalid slot number for
local variable (0) at
net.sf.saxon.expr.XPathContextMinor.setLocalVariable(XPathContextMinor.java:362) at
net.sf.saxon.instruct.LocalVariable.processLeavingTail(LocalVariable.java:20) at
net.sf.saxon.instruct.Instruction.process(Instruction.java:93) at
fleetcycle.ui.xslcomponents.Panel$PanelInstruction.process(Panel.java:117) Can you
please comment on the feasibility of this project I am undertaking? If there are
alternatives that I am not thinking of that would be helpful to know as well. [1]:
http://saxonica.com/documentation/extensibility/instructions.html
Legacy ID: #7951149
Legacy Poster: Michael Kay (mhkay)
Your analysis is basically correct. The interface for writing extension instructions
is low-level, poorly documented, and lacks robustness. In fact, it's not really an API
in any meaningful sense of the word; you pretty well have to write your code as if it
were part of the Saxon internals. I would like to do a cleaner API, along the lines of
the new interface introduced in 9.2 for writing integrated extension functions; but it's
not really very high on the agenda, given that not many people are trying to write such
extensions.
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