This article may be of help to you:
The full article on scope can be found here: https://community.tealiumiq.com/t5/iQ-Tag-Management/Extensions/ta-p/13649
However here is a TL;DR version
The other scopes are:
DOM Ready - Will fire when the browser reaches the DOM Interactive / DOM Ready stage
All Tags Scope - Extension will run when a view or link event happens
Tag Scoped - The extension is only called if the tag is loaded, and will run in the scope of the tag.
Additionally, for All Tags Scope, you have the additional options:
Before Load Rules - Will process an extension before load rules are processed. Ideal for setting load rule conditions
After Load Rules - Default, Used for setting data up for tags
After Tags - Effectively the opposite of Preloader. Will fire once the tags have finished, and called their send method.
In addition, there are also Run Once options for these, whereas the name suggests these will only run once.
Run Once after Load Rules
Run Once before Load Rules
Run Once After Tags
I hope that helps explain Preloader and scopes in general.
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