Q:

Should Tag Manager's snippet be officially entered into the head or body?

Google Analytics' https://support.google.com/analytics/answer/1008080 states:

Paste your snippet (unaltered, in its entirety) into every web page you want to track. Paste it immediately before the closing  tag.

But what about Tag Manager? Is there an updated official documentation about whether it should be in the head or body (and where exactly in the head/body)?

A:

Thanks @Pechou, turns out there's also https://support.google.com/tagmanager/answer/6103696

Adding the Container Snippet
Paste this code so that it appears immediately after the opening <body> tag on every page on your site.

