[wyattpeak]

EDIT: Never mind, sorry, I missed part of the article, it does indeed say what you say.

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That's the opposite of what your source says:

> In writing, however, use to in place of used to is an error.

Used to X was the standard past tense of to use in the sense of being in the habit of:

I used to fish: I was previously in the habit of fishing, correct both in the past and today.

I use to fish: I am presently in the habit of fishing, correct in the past but no longer understood today.

The second, however, is according to MW occasionally misused to mean "I was previously in the habit of fishing".

[as_bntd]

There's a difference when use is preceded by did:

> The problem becomes a little trickier in constructions with did. The form considered correct following did, at least in American English, is use to. Just as we say "Did he want to?" instead of "Did he wanted to?," so we say "Did he use to?" instead of "Did he used to?" Here again, only in writing does the difference become an issue.

> While in American English "did used to" is considered an error...

Personally, didn't used to looks jarring, but it made me open the article so…

[wyattpeak]

Oh, excuse me, I entirely missed that section of the page. Makes sense there's a geographical distinction, I'm not American so I suppose I don't have the intuitive issue with it, but on reading I see the logic.