I wrote following code (https://secure.phabricator.com/w/test/)
lang=html
lang=c++
#include <hello>
int main() {
}
{F10510, size=full, layout=right, float}
lang=c++
#include <hello>
int main() {
}
and preview shows following.
{F989538}
actual saved page show following.
{F989541}