Add <parameter> tag definition and its attributes

[skrantzman]

I would like to see a section of the help file dedicated to the <parameter> tag. The parameter tag is mentioned periodically throughout the help documentation as a child tag, for such tags as ListDataSource and DetailDataSource. However if you do a search in the help documentation for "parameter" the resulting hits do not pertain to this tag.

I feel that this is a very misunderstood tag. Here are some examples that I think many XMP user would benefit from some clarity on:

1. In examples throughout the documentation,, sometimes I see that they include the "Value" attribute, and sometimes they don't. A clear explanation of when the value attribute is, or is not needed would be helpful.
2. I still do not understand the "Alias" attribute. I don't know when or why to use it. The only time I do use it, is after failed attempts to return data form a ListDataSource, or DetailDataSource tag. On occasion when troubleshooting, I throw in the alias attribute, and the DataSource suddenly returns data. Why is that?
3. Until recently (just last week) I did not fully understand why I should use the "DefaultValue" attribute. I added the following parameter to the DetailDataSource tag of a volunteer profile form: <Parameter Name="UserId" value='<%#FormData("vid")%>' DefaultValue='<%#UserData("ID")%>'/> This way I can use the same form to allow a volunteer to update their profile, or I can redirect a admin to this page to update a volunteer. Extremely useful in only having to maintain one form..
4. DataType. This is an optional attribute. When should it be used?

Clear explanations and examples of these would go a long way to help XMP users fully understand how to use this extremely valuable tag correctly.