The steps for makeCredential do a bunch of implicit getting of members

[bzbarsky]

For example, this bit:

If timeoutSeconds was specified

What this really means is "if the timeoutSeconds member of options is present" where "is present" means https://heycam.github.io/webidl/#dfn-present. There's an attempt to deal with this by having "timeoutSeconds" be a link to the relevant dictionary member of the relevant dictionary, but it's still a bit confusing when one is just reading the text.

There are various other examples along these lines here.