We write our documentation in an informal tone, so use most types of contractions.
In particular, it's fine to use -n't contractions, such as isn't, don't, and can't.
One reason that such contractions are useful is that it's sometimes easy for a reader to miss the word not, whereas it's harder to misread don't as do.
Noun + verb contractions
In general, avoid contractions formed from nouns and verbs.
Recommended: The browser is fast, simple, and secure.
Not recommended: The browser's fast, simple, and secure.
The first example is better because using 's in place of is could cause the reader to think that browser's is the possessive form.
In some cases, it's OK to use a noun + verb contraction, such as If you want to display information, a table's your best option. However, in general, it's best to avoid that kind of contraction.
Recommended: The following guides are a good way to learn to use Universal Analytics.
Not recommended: The following guides're a good way to learn to use Universal Analytics.
Here, guides're just sounds clunky and weird.
Don't use double contractions
Double contractions contain not just one but two contracted words. Some examples of double contractions are as follows:
- mightn't've (mightn't have → might not have)
- mustn't've (mustn't have → must not have)
- wouldn't've (wouldn't have → would not have)
- shouldn't've (shouldn't have → should not have)
Its and it's
Don't confuse its (possessive) with it's (noun + verb). It's just not right!