@egreg I really have no idea what I'm looking at (nor what I'm supposed to understand) :(

@Manuel Don't worry, then: \leaders are quite funny at times.

@Manuel Try switching \hrule and \vrule in the code above and something should be clearer.

@egreg And \rule is basically \leavevmode\vrule depth #1 width #2 height #3\relax?

@Manuel Almost, yes. It has optional arguments, though.

@egreg I will learn that some day, never undestood the need for \vrule and \hrule, may be just because of the \leaders? If it weren't for the \leaders it could work just with \vrule?

By the way, why is \hrule height 0pt needed before \leaders\hrule.

I tried \begin{array}{cc}{...}\end{array}. Also didn't work.

Ah, never mind. Brain cancer.

@Manuel No, \hrule has its uses; LaTeX avoids it because it's difficult for a “normal” user.

@Manuel Glue is removed at a page break (and the start of the document is a page break). The invisible \hrule masks it.

It's basically the trick used by \vspace*

@egreg and the tick...

@DavidCarlisle People should know better. :(