Google Spreadsheets Functions
Google Sheets (spreadsheets) allow you to use many functions available in other spreadsheet software. Excel and Open office for example have many calculation functions, such as =SUM() =AVERAGE() .
Google functions are a set of Google specific functions. Some Google functions using Xpath to call specific information from xHTML and XML webpages.
In Google Docs (spreadsheet) "Insert" > "Function" > "More" > "Google" > Select the Google Function/Copy the reference function code (eg. =GoogleClock() )
Xpath Examples [finding the general path to a webpages information eg. ALL image URLs on a webpage]
Xpath is way to call specific information from a XML or xHTML webpage. Xpath is similar to technologies such as XMLRPC and AMF (and older cell based DDE ), but simpler and more accessible for non programmers.
Xpath can call information directly into a spreadsheet cell (maybe directly in a markup language in future) from a online source. Once there are enough specific tags in the online document, any publicly live data can be obtained.
xPath Standards: [Google Docs xPath may differ slightly]
W3schools Xpath Introduction
Public Data - W3schools Xpath Syntax
Public Data - W3C - XML Path Language (XPath) Version 1.0
Non Public Data - Google Secure Data Connector
Live Information in a Spreadsheet.