Is there a way to check if a custom form element exists in application Suppose i am building a custom form element with 


  hook_element_info()


Is there a way , in another module,to check this element's existence before inserting it to a form?
You can invoke the hook yourself to check for the existence of a specific element type:

if (in_array('some_element_key', array_keys(module_invoke_all('element_info')))) {
  // The element type exists.
}