def is_visible(self,locator):
return self.get_boolean("<STR_LIT>", [locator,])<EOL>
Determines if the specified element is visible. An
element can be rendered invisible by setting the CSS "visibility"
property to "hidden", or the "display" property to "none", either for the
element itself or one if its ancestors.  This method will fail if
the element is not present.

'locator' is an element locator