Correct way of linking arabic numerals and their written-out variants (in official documents)*

Question

In official documents, numbers are first written in arabic numerals, and then they are immediately written out with words. This is to make certain no fraud can be made. (I assume.) What is the correct way of doing this? The two forms have to be linked with a word, don't they?

Example: "$1234... one thousand two hundred thirty four dollars"

In place of the dots, should you write "that is,"? (Putting a comma between the arabic numerals and "that", like so: "$1234, that is, one thousand two hundred thirty four dollars".)

Should I just put the written-out variant in parenthesis?

Example: "$1234 (one thousand two hundred thirty four dollars)"

I hope my question is clear. :)

*If a separate rule is valid in non-official documents, please be so kind as to explain that as well.

Answer 1

It would be acceptable and preferred to do just as you said:

Example: "$1234 (one thousand two hundred thirty-four dollars)"

(Note the hyphen in "thirty-four". American usage would call for "$1,234", while other regions may not prefer the separating comma.)

Note that in ordinary writing without currency, or lower numbers, you might want to use the opposite order, such as:

Twelve (12) goats, five (5) golden rings, four (4) calling birds, three (3) French hens, two (2) turtle doves.

This is commonly seen in legal documents, contracts, disclaimers, contest rules, and so forth.

Answer 2

For what it's worth, the U.S. Government Printing Office (GPO) Style Manual (PDF)¹ says, in paragraph 12.18 (on page 290):

A spelled-out number should not be repeated in figures, except in legal documents.  In such instances use these forms:

• five (5) dollars, not five dollars (5)
• ten dollars ($10), not ten ($10) dollars

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¹ subtitled "An official guide to the form and style of Federal Government printing"