isValidXpathQuery(query) checks the validity of an XPath query string.
  
    Parameters
- query
- 
              The XPath query string to check. 
Returns
Returns true is the query is a valid XPath query string, false otherwise.
Example
The method can be used to check the validity of a XPath query prior to use:
if (search.isValidXpathQuery(query)){
    nodes = search.xpathSearch(query);
}
else {
  // ...
}
      
    