This is one of the simplest to get right and yet is often wrong as the result
of things being specified on the fly and not revisited later. The typical
example is SVG having
rect instead of
rectangle. It rarely has a serious
impact, but it does make a language harder to learn.
One thing that is difficult when introducing a new feature inside a language is to make sure that it works coherently with all the rest of the language's features. Such errors are often difficult to detect without extensive testing.
A good example is the different treatment applied to shapes and animations in SVG.
The following will work and display a second rectangle inside the
But the following, while valid, will not cause the
g element to be
defs will be animated, which will do nothing. This sort of
discrepancy confuses authors, many of whom will try the latter at some point. While
extensive testing is often too costly to put into effect, one low-tech approach that
can help is to have a matrix tabulating all the features against all the others, and
for each one that is added to look at how they interact. This would have made it
apparent that animations applied to
use work (they can animate it), but
use applied to animations doesn't. How to address this, if only by clearly
documenting it, is then a matter that will depend on the situation.