What is <!-- thelevel[start]::HeaderContent -->, and how can it be edited?
The site template can be edited, but the comments that all start with the level are hooks into cms functionality and get replaced by the resulting cms layout templates. They should not be removed or modified. They can, however change location in the file. The HeaderContent comment hooks into the cms for all the html output such as the logo, site title, search, and login area. The NavigationContent comment hooks into a more complex feature with the cms that defines the top level navigation links. You can't edit the boilerplate to change what the outputs of those cms hooks are, but you could for example, move [email protected]="tools" and the child comments comments below [email protected]="navigation" and things would still work.