Most of this looks quite good!
The only part that throws me for a loop is in the Grammar section, which contains a mix of best practices (like "Prefer active voice to passive voice") mixed with basic rules about subject-verb agreement. The former is what I would expect to see in a Style Guide, while the latter is, I dunno...what I would expect as a basic requirement for passing high school English?
It just feels like for the level of fluency presumably required for a Technical Writer, basic grammar rules should be well understood and not need to be explicitly stated.
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