English verbs are pretty simple. We don’t have a complex system of verb endings, as many languages do, and we have relatively few irregular verbs. But English still has an elaborate system of tenses, aspects, voices, and moods. Keeping them all straight can be difficult if you don’t know the terminology.
"Sap of trees such as the sugar maple can be reduced into sugary syrup for pancakes."
Do you feel an urge to insert commas? Those who know syrup, or who know trees, understand why that would be wrong.
There is no grammatical need to place a comma before every occurrence of "such as," and sometimes a preceding comma is wrong. Sometimes "such as" is used restrictively, not to provide a parenthetical example:
Editors, such as Adrienne, say so. = Adrienne is an example of an editor. Editors such as Adrienne say so. = Only editors who are like Adrienne.
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