Using AquaPath is simple! Open an existing XML document (of any type) or even author an XML document using AquaPath itself (AquaPath is also a rudimentary text editor). The source text of your XML document appears under the "Source" tab in an AquaPath document window... use this tab to author or edit your document.
Next, type an XPath expression into the "XPath" textfield at the top of the AquaPath document window. Click "Evaluate" to see the matching node sequence. You will see a status bar message just below the XPath text field showing either the number of nodes in the result sequence or and error message if your XML document is not well-formed or if your XPath expression is invalid.
Under the "Results" tab, you will find a text area containing the string value of the result sequence. The whitespace of each node has been compressed so that you will see a single node's string value per line. This tab's contents are convenient for copy-pasting the results to another text editor or wherever.
The "Display" tab is where all the magic happens. Here you will see a dynamic (DHTML), syntax-colored representation of your XML document with "-" or "+" signs next to each element node. Use these symbols for collapsing and expanding a given element and its children. Also, all nodes and text matching your XPath expression will be highlighted in yellow. Cool!
AquaPath is implemented using Apple's Cocoa/Objective-C NSXML Framework. NSXML supports a large subset of XPath 1.0. XPath 2.0 is not currently supported by AquaPath. If anyone knows of an open source C or C++ -based XPath 2.0-aware library, shoot me and email, and I'll update AquaPath with XPath 2.0