There's an interesting issue with invisible fonts that hasn't been pointed out in the comments thus far. In a job interview last year, I was asked to name some

There's an interesting issue with invisible fonts that hasn't been pointed out in the comments thus far. In a job interview last year, I was asked to name some ways to hide an element on a page. I think I came up with seven or eight ways and listed upsides and downsides of each. Besides obvious ones like opacity, visibility, display: none, z-index, moving the elements off-screen, setting font-size to 0, etc., one idea I came up with on the spot was to design a font with blank characters in case the div was simply text. The text would be visible to search engines but not to users. (Since I was interviewing at a large search company, I also raised the point that they might want to start analyzing custom fonts to make sure they're not simply empty characters, if they're not already.)