protected FormState::isRequestMethodSafe()
Checks whether the request method is a "safe" HTTP method.
http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1 defines GET and HEAD as "safe" methods, meaning they SHOULD NOT have side-effects, such as persisting $form_state changes.
bool
\Symfony\Component\HttpFoundation\Request::isMethodSafe()
protected function isRequestMethodSafe() { return in_array($this->requestMethod, array('GET', 'HEAD')); }
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