Write more documentation

.docs/content/3.In-depth/0.sources-and-embeds.md

@@ -1,6 +1,11 @@
 # Sources vs embeds
 
+::alert{type="warning"}
+This page isn't quite done yet, stay tuned!
+::
+
+<!--
+TODO
 - How do sources and embeds differ
 - How do sources and embeds interact
-
-TODO
+-->

.docs/content/3.In-depth/1.new-providers.md

@@ -1,7 +1,12 @@
 # New providers
 
+::alert{type="warning"}
+This page isn't quite done yet, stay tuned!
+::
+
+<!--
+TODO
 - How to make new sources or embeds
 - Ranking
 - Link to flags
-
-TODO
+-->

.docs/content/3.In-depth/2.flags.md

@@ -1,6 +1,10 @@
 # Flags
 
-- what are flags?
-- list of all flags and their meaning
+Flags is the primary way the library seperates entities between different environments.
+For example some sources only give back content that has the CORS headers set to allow anyone, so that source gets the flag `CORS_ALLOWED`. Now if you set your target to `BROWSER`, sources without that flag won't even get listed.
 
-TODO
+This concept is applied in multiple away across the library.
+
+## Flag options
+ - `CORS_ALLOWED`: Headers from the output streams are set to allow any origin.
+ - `IP_LOCKED`: The streams are locked by ip, requester and watcher must be the same.