What is the full syntax of Groovy's GPath expressions?

While trying to parse RSS feeds in Groovy, I found a GPath example using wildcards:

def text = """ 
<data> 
   <common-tables> 
    <table name="address"/> 
    <table name="phone"/> 
  </common-tables> 

  <special-tables> 
    <table name="person"/> 
  </special-tables> 

  <other-tables> 
    <table name="business"/> 
  </other-tables> 
</data> 
""" 

def xml = new XmlParser().parse(new ByteArrayInputStream(text.getBytes())) 
def tables = xml.'**'.table.findAll{ it.parent().name() == 
"special-tables" || it.parent().name

(from http://old.nabble.com/Q:-Avoiding-XPath---using-GPath-td19087210.html)

It looks like a funny use of the 'spread-dot' operator. I can't find any reference to this on the Groovy site, books, etc开发者_开发百科.

How does this work, and more importantly, how do you discover this? Is there any XPath to GPath 'Rosetta Stone' out there?

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Well, as usual, the best place to find information is in the Groovy source itself.
The result of a parsing is a groovy.util.slurpersupport.GPathResult object.

If you look at the source (plain java file), you'll see that the getProperty(string) method has the following special operators:

• ".." that returns the parent
• "*" that returns all the children
• "**" that act as a depth first loop
• "@" that is used to access a property
• the normal node accessor.

That's all, no other magic keywords for the moment.

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All of those strings are treated as properties. None of them are actually operators.

The calls are routed through GPathResult#getProperty which specifically checks for the operators listed in gizmo's answer.