The Xojo Doc site has several thousand pages of information. To make it easier to quickly find things in the online docs, topics are categorized. You can find categories that a topic belongs to at the bottom of its page. Here are several useful categories to start with.
API 2.0
You can use this category to show all API 2.0 items across all releases, which is quite useful with the release of 2019r2:
https://documentation.xojo.com/Category:API_2.0
All Deprecated
Use this category to show all deprecated items across all releases:
https://documentation.xojo.com/Category:Deprecated
All Deprecated for a single release
This category to shows all deprecated items for a specific release:
https://documentation.xojo.com/Category:Deprecated2019r2
Change the release value to see other releases.
All New for a single release
Use this category to show all new items for a specific release:
https://documentation.xojo.com/Category:New2019r2
Change the release value to see other releases.
Show All User Guide topics
This category displays all pages that are part of the User Guide:
https://documentation.xojo.com/Category:User_Guide
Show All Categories
There are many more categories. You can use this link to see them all:
https://documentation.xojo.com/Special:Categories
Or as mentioned earlier, at the bottom of each topic page you can view the list of categories to which it belongs. Jumping to other categories can help you find other related information for quickly.