In a recent answer I've tried to hide some text. Unfortunately, something seems broken.

Here's the not-so-hidden text:

! Let $X$ be the set of complete theories that satisfy "everything is countable" and have unboundedly many $\alpha<\omega_1^L$ with $L_\alpha$ realising them. The theory of $L_{\omega_1^L}$ is one such theory, and we will be done if we prove that there are some others. Now $X$ is a definable class in $L_{\omega_1^L}$, and so it must have some other elements or else $L_{\omega_1^L}$ would admit a truth defintion ($\varphi$ is true in $L_{\omega_1^L}$ iff the unique element of $X$ contains $\varphi$).

I'm not sure what the bug is. The plain-text version of the passage also doesn't hide properly:

! let X be the set of complete theories that satisfy "everything is countable" and have unboundedly many \alpha<\omega_1^L realising them. the theory of L_{\omega_1^L} is one such theory, and we will be done if we prove that there are some others. but X is a definable class in L_{\omega_1^L}, and so it must have some other elements, or L_{\omega_1^L} would admit a truth defintion (\phi iff the unique theory in X satisfies \phi).

But spoilering latex seems to work fine:

This is some latex! $X$ $L_{\omega_1^L}$