Numbers in accepted usage
Spell out numbers for generally accepted usage, such as idiomatic expressions.
The word one frequently appears in text without referring to a quantity; it may appear awkward to express it as a numeral and therefore it should be spelled out.
When one may be replaced by a or a single without changing the meaning, the word one rather than the numeral is appropriate, in addition to spelling it out when used as a pronoun.
Other numbers - most frequently zero, two and large rounded numbers - also may be written as words in circumstances where use of a numeral would place an unintended emphasis on a precise quantity or would be confusing.
The study was confounded by one problem after another.
We move from one extreme to another.
The outcome was a zero-sum gain.
There are at least two sides to every issue.
Please include an example or two in the documentation.
The vaccination effort has involved tens of thousands of volunteers injecting over half a million people.
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