ImportXML lets you get information from filetypes such as xml, html, csv, tsv, as well as RSS and Atom feeds.
This example in Google Docs Help for importXml function -
=importXml("toysrus.com";; "//a/@href")
... fails with this message -
error: The xPath query given could not be evaluated. Please check the syntax of the query: //a/@href
There are 2 other cases where they ran well earlier but now fail. The function scrapes well in this case.
Are there any changes in the way ImportXML function works in Google Docs Spreadsheet that makes it fail in some cases?