code: @Nullable
    private static XPathExpression _compileXPath (@Nonnull final XPath aXPathContext,
                                                  @Nonnull final String sXPathExpression) throws XPathExpressionException
    {
      XPathExpression ret = null;
      try
      {
        ret = aXPathContext.compile (sXPathExpression);
      }
      catch (final XPathExpressionException ex)
      {
        // Do something with it
        throw ex;
      }
      return ret;
    }
docs: Compile an XPath expression string to an {@link XPathExpressionException}
  object. If expression contains any variables, the
  {@link XPathVariableResolver} will be used to resolve them within this
  method!
  
  @param aXPathContext
  Context to use. May not be <code>null</code>.
  @param sXPathExpression
  The expression to be compiled. May not be <code>null</code>.
  @return The precompiled {@link XPathExpression}
  @throws XPathExpressionException
  If expression cannot be compiled.