I'm trying to extract some data from online htmls using ruby hpricot library. I use the firefox extension fire bug to get the xpath of a selected item.
There's always the extra tbody tag present in the produced xpath expression. In some cases, I must remove the tbody tag from the expression to obtain the results while in other cases, I must keep the tag to get the results.
I just can't figure out when to keep the tbody tag and when not to.
In order to take into account and avoid this problem, use XPath expressions of the following kind:
/locStep1/locStep2/.../table/YourSubExpression
|
/locStep1/locStep2/.../table/tbody/YourSubExpression
If the table doesn't have a tbody child, then the second argument of the union operator (|) selects no nodes and the first argument of the union selects the wanted nodes.
Alternatively, if the table has a tbody child, then the first argument of the union operator selects no nodes and the second argument of the union selects the wanted nodes.
The end result: in both cases the wanted nodes are selected
Well with HTML 4 or with XHTML served as text/html the parser always infers a tbody element to wrap tr elements in that are direct children of an table element in the parsed mark up, that is why inside the browser DOM a HTML table always has a tbody containing any tr elements and a tool like Firebug gives you path that works against the Firefox/Mozilla DOM. I don't know what kind of parser your Ruby library uses, perhaps it uses an XML parser for XHTML documents and an XML parser does not infer tbody elements for table elements.
HTML5 always adds the tbody element if its not there explicitly - it's part of the repair strategy for dealing with invalid HTML. If you want to cope with a variety of environments, using table//tr might make sense.
来源：https://stackoverflow.com/questions/8203619/tbody-tag-in-xpath-produced-by-fire-bug