Move rules about expressions before rules about avoiding fake ES6 & parent.tag

[jbmoelker]

Summary

Since markup is typically written before script, the rules about expressions should come before the rules about script.

Proposed changes:

• Move rules about expressions before rules about avoiding fake ES6 & parent.tag.
• This is just a re-order, no new content is added.

  Checklist

• [X] The changes are in style guide format.
• [X] The changes can be merged into the target branch without conflicts.