The following lines test various combinations of letter-spacing (especially negative values) and opacity. All of the lines should say "Hello, world" but the spacing and background shading will vary from test to test. The W3C specs are fairly silent on how user agents should handle unusual values of letter-spacing, especially negative ones, which are explicitly implementation-dependent. Different browsers will render these differently, but hopefully the WebKit ports will be consistent, at least.
The first line should be normally spaced.
Hello, world
The next line tests a slight positive letter spacing, and should be slightly spaced out (wider than normal).
Hello, world
The next line tests a large positive letter spacing, and should be *very* spaced out. You may only see an 'H' and a 'w', perhaps on two different lines, unless you scroll way to the right.
Hello, world
The next line tests a very large positive letter spacing, and should also be *very* spaced out. You may only see an 'H' and a 'w', perhaps on two different lines, unless you scroll way to the right.
Hello, world
The next line tests a small negative line spacing, and should be crammed backwards
Hello, world
The next line tests a large negative line spacing, and should be just display an 'H'
Hello, world
The next line tests a very large negative line spacing, and should just have an 'H'.
Hello, world
The next few lines test the interaction with opacity. The first line should be normally spaced out, slightly opaque, and on a differently-colored background
Hello, world
The next line tests a small positive line spacing, and should be slightly spaced out, opaque, and on a background.
Hello, world
The next line tests a large positive line spacing, and should be very widely spaced, on a background.
Hello, world
The next line tests a very large positive line spacing, and should be very widely spaced but blank, and on a background.
Hello, world
The next line tests a small negative line spacing, and should be blank.
Hello, world
The next line tests a large negative line spacing, and should be blank.
Hello, world
The next line tests a very large negative line spacing, and should be blank.
Hello, world
Now we do a few basic right-to-left tests:
The first line should be normally spaced.
Hello, world
The next line should be slightly spaced out (wider than normal).
Hello, world
The next line should be crammed backwards, just as if it wasn't right-to-left
Hello, world
The next line tests a large negative line spacing, and should just print a 'd'
Hello, world
Now, opacity as well - The next line should be printed right to left, slightly spaced out (wider than normal), and on a background.
Hello, world
The next line tests a small negative line spacing, and should be blank.
Hello, world
The next line tests a large negative line spacing, and it should be blank.
Hello, world