Extract attribute's value with XPATH in a special case

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hi i need help to extract information from XML with xpath.I will use Xpath to extract the value of the attribute of one Tag that start with a generic keywork:\[code\]<st:Testprova id='abcd'> ....</st> or<st:Test1prova id='defg'> ....</st>\[/code\]I used that Xpath expression:\[code\]"//*[contains(.,'prova')]/@ID"\[/code\]but does not work. Can you help me??