Looks like I understood the reason. It's not visible because it's inside
the margin, and wiki does margins. :) Am I right?
The following example does not work properly in wiki (the rule is
missed), while in mkIV it's OK.
The sound of a duck is a good demonstration of how different people
listen to a sound. Everywhere in Europe the sound is equal. But in
every country it is described differently: kwaak||kwaak (Netherlands),
couin||couin (French), gick||gack (German), rap||rap (Danish) and
mech||mech (Spanish). If you speak these words aloud you will notice
that in spite of the consonants the sound is really very
well described. And what about a cow, does it say boe, mboe or mm?
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