IN Line 1 on Page 1 or ON Line 1 on Page 1?

Is it IN or ON?

Very confused. Please help!
in a line
In my opinion, if this is a "form" to be filled out, and the [blank] lines are numbered (eg, a tax return form), the instructions would say "enter the name of your spouse on line 1."

If you're looking at a newspaper article, you might say, "There's a misspelling in line one," referring to a line of print.
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It's the latter.

I am looking at an article (a law). So I would like to say "in lines 2 and 3 of Article 2, blah blah blah."

But I see people writing ON lines 2 and 3 of paragraph 1... So I am confused.

Please help!
in lines 2 and 3 of Article 2
Agreed. These are lines of text, not lines to be written on.

The original question was unspecific as to "lines of text" or "lines in/on a form."

Quoting from literature of the venerable IRS (whose otherwise unemployed attorneys generally manage to avoid the preposition altogether):

If your Form 1099-R shows a larger amount, use the amount on this line instead of the amount from Form 1099-

If you are a retired public safety officer, see Insurance premiums for retired public safety officers on page 23 before entering an amount on line 12b .

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Thank you everyone. Now I can write with confidence! Thanks again.