Alert commandline ConsoleTask Criteria syntax

Question

Hi,
I have alerts generated by rules and monitors. This alerts may or may not contain additional data in its CustomField1: URL to a web page with some details.
I have created an alert command line console task (and category) in my Management Pack.
This task opens an URL from alert's CustomField1 in default web browser. I can easy pass this value to the task arguments just using $CustomField1$ syntax:
<ManagementPackFragment SchemaVersion="2.0" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Categories>
<Category ID="MyMP.OpenUrlTaskCategory" Target="MyMP.OpenUrlTask" Value="System!System.Internal.ManagementPack.ConsoleTasks.Alert" />
</Categories>
<Presentation>
<ConsoleTasks>
<ConsoleTask ID="MyMP.OpenUrlTask" Accessibility="Internal" Enabled="true" Target="MyMP.MyClass" RequireOutput="false">
<Assembly>MyMP.OpenUrlTaskAssembly</Assembly>
<Handler>ShellHandler</Handler>
<Parameters>
<Argument Name="WorkingDirectory" />
<Argument Name="Application">cmd.exe</Argument>
<Argument>/c "start "" "$CustomField1$"</Argument>
</Parameters>
</ConsoleTask>
</ConsoleTasks>
</Presentation>
<Resources>
<Assembly ID="MyMP.OpenUrlTaskAssembly" Accessibility="Internal" FileName="MyMP.OpenUrlTask" HasNullStream="true" QualifiedName="MyMP.OpenUrlTask" />
</Resources>
</ManagementPackFragment>
Task works fine, it opens a link in default browser. But now I want to use optional <Criteria> for my Console Task to show it only if CustomField1 actually is not empty and contains something that starts with 'http://'
I have no idea how to access Alert's CustomField1 value in the Criteria XPath expression. I have tried a lot of options with $CustomField1$, /CustomField1, /Property[Name='CustomField1'] and so on. But it seems that Alert schema is not so primitive.
What is a valid syntax in the Criteria to verify that Alert's CustomField1 is not empty and matches some pattern (I believe XPath function fn:starts-with() should work when I can correctly get the value)? MSDN example is not very descriptive in this case.
Thank you for any help.
Andrey.

Answer 1

Juke, thank you for the answer.
I have read MSDN examples and I know how does XPath work. The question is a bit deeper: I want to show my console task only for alerts that satisfies the following conditions:
1. targeted to specific monitoring class from my pack (or, if possible, generated by specific rules)
2. containing URL in it's CustomField1
My current code is based on
this MSDN example (that is actually related to SCSM, not SCOM). There is also another MSDN article related to SCOM SDK (here I can specify consoletask category using "Category"
attribute) but it doesn't work at all (can't be compiled with VSAE - it says that "Category" attribute is not valid)
Anyway, now with my code (from the first message in thread) I see the console task for
any Alert in SCOM (even for Alerts that are not related to MyMP.MyClass objects, e.g. for Alerts targeted to Windows Computer and so on). I believe that correct <Criteria> should help me to fix it.
The question is: Is it possible to somehow reach selected Alert's properties (e.g. CustomField1) using XPath in criteria? To do it I should know serialized Alert's schema.
Also: why do I see this task in the SCOM console for all alerts but not only for alerts generated against MyClass? As you can see I have specified "target" attribute for the task. MyClass is based on ApplicationComponent
Thank you