Draft an internal style guide entry for a specific writing rule

You maintain the editorial style guide for a WordPress plugin company's blog.
Writers keep inconsistently mixing numerals and spelled-out numbers in posts ("we
tested 3 plugins" next to "we tested seven configurations" in the same article),
and you need a style guide entry that actually settles it instead of a vague "use
your judgement" note.

RULE TOPIC: [numerals vs spelled-out numbers in body copy]
CURRENT INCONSISTENCY: [writers mix both within the same post, no shared rule
exists]
EXISTING STYLE GUIDE FORMAT: [each entry has a Rule line, a Why line, 2 examples,
and an Exceptions line]

Work through this before drafting the entry:
1. State one clear, memorable rule (spell out one through nine, use numerals for 10
   and above), not a rule with so many conditions writers won't remember it under
   deadline.
2. Explain the "why" briefly, readers scan faster with numerals for larger, more
   noteworthy figures, and spelled-out small numbers read as smoother prose, so
   writers understand the reasoning rather than just memorizing an arbitrary rule.
3. Edge case: the general rule breaks down for percentages, version numbers, and
   sentence-starting numbers. Percentages are always numerals regardless of size
   ("3%" not "three percent"), version numbers are always numerals ("WordPress 6"),
   and a sentence should never start with a numeral, rephrase the sentence instead
   of spelling out a large number awkwardly at the start. Each of these needs its
   own explicit line since the main rule doesn't cover them.
4. Note where the rule should flex: in data-heavy posts or tables with lots of small
   numbers next to each other, consistency within that specific table/list matters
   more than the general rule, use numerals throughout that section if mixing would
   look inconsistent side by side.
5. Pull 2 realistic before/after examples showing a sentence with the inconsistency
   fixed.

Format the output to match the existing style guide entry format: Rule, Why,
Examples (before/after), Exceptions.

Replace the bracketed rule topic, inconsistency, and format above with your own.