Sitefinity add new function to page text editor - radeditor

Question

I can find a lot of documentation on how to add things to the text editor itself, including a place to add additional buttons/functions into the XML through the admin settings.
What I cannot find is where I would then create the new functions that those settings reference. I tried searching my local solution for a few random ones and nothing came up.
For clarification, I'm looking at adding in a button on the editor for pages - or really anywhere in the back end that uses the text editor, but at least in pages. I'm not trying to add a completely new editor in my own widget or something, which would make this really easy as it appears those can simply be declared inline.
Update
Going to Administration -> Settings -> Text editor and clicking "edit" for "Default tool set" gives me a settings XML sheet something like this. I should be able to just add a new tool here in the XML, but I have no idea where the actual code for that tool should live in order to be used by this editor.
<?xml version="1.0" encoding="utf-8" ?>
<root>
<modules>
<module name="RadEditorStatistics" dockingZone="Bottom" visible="false" />
<module name="RadEditorDomInspector" visible="false" />
<module name="RadEditorNodeInspector" visible="false" />
<module name="RadEditorHtmlInspector" visible="false" />
</modules>
<tools name="MainToolbar">
<tool name="ToggleAdvancedToolbars"/>
<tool name="Bold" shortcut="CTRL+B"/>
<tool name="Italic" shortcut="CTRL+I"/>
<tool separator="true"/>
<tool name="InsertOrderedList" />
<tool name="InsertUnorderedList" />
<tool separator="true"/>
<tool name="LinkManager" shortcut="CTRL+K"/>
<tool name="Unlink" shortcut="CTRL+SHIFT+K"/>
<tool name="ImageManager" shortcut="CTRL+G"/>
<tool separator="true"/>
<tool name="AjaxSpellCheck"/>
<tool separator="true"/>
<tool name="PasteFromWord" />
<tool separator="true"/>
<tool name="FormatBlock"/>
</tools>
//...
</root>