Hi @wisskid, is there any interest in this fix? 4.x also needs this fix IMO.

I think so. Can you clarify the actual error this causes?

The function: htmlspecialchars(string $string, ....), the first argument's type is string (PHP is more and more strict about typing)

But {$foo+$bar} would result in non-string type:

$ php -r 'echo gettype( (string)1+2 );'
integer%

So, it needs to use htmlspecialchars((string) ({$output}), to make sure the type is string:

$ php -r 'echo gettype( (string)(1+2) );'
string%