Q: Do XPath queries work with HTML?
A: XPath works on XML and (X)HTML. Poorly formatted markup (i.e. markup that fails to parse because of errors) can possibly be fixed with Tidy.

Q: Is there any way to update the nodes that were created on the first import?
A: If the GUID or URL is set to a unique id, then setting import to replace or update should work.

Q: Is there an easy way to generate XPath queries?
A: See the documentation for Firefox/Firebug add-ons and other javascript bookmarklets.

Q: What is the context argument?
A: It defines the scope for the XPath arguments. The scope is defined via an XPath argument. Use the context argument to define your "working area" in a XML documents structure. The context narrows down the scope of information you're working with. By defining the context, the later XPaths can be simpler because they can assume they are working within the context.

This is analogous to working with directories and files. You use "cd /colors" to select a position where you start your work (a context). Now that you've set your context (to "/colors"), you don't have to keep specifying /colors; all following work is assumed to be under the "/colors" directory. Now you can do a "dir" to see all the files in /colors "red, blue, orange, purple,...". Since you are within the colors context (or directory in this analogy), you only have to do a "dir red", to see "fireengine, mauve, vermillion,..." or "dir blue" to see "navy, baby, sky, bluebell,.." without having to keep mentioning /colors because all the following commands use the context setup by "cd."

Q: Can queries be made outside the context?
A: Yes, see #900632: Grab value from outside the context section of XML... At all possible?. Use an XPath with an absolute expression, such as using "/" at the beginning.

Using the file analogy started in the above discussion about context, if you set your context to colors by "cd /colors", you can look outside of your context by doing a "cd /users" by starting with a "/". XPath syntax isn't exactly the same as navigating file structures but there are similarities.

Q: The only available drop down entry is "XPath Expression" but I don't see any place to enter tags. Is there a problem?
A: No. Queries are entered on the node form when creating a source. They can also be set in the Parser settings. The values set in Parser settings are used as default settings for every feed node created.

Q. Are default namespaces supported?
A: The default namespaces declared in a document are automatically registered before performing an XPath query. So any queries that use a default namespace should work without user intervention. Namespaces with a prefix are used as normal.