The ArcGIS Explorer add-in file (.eaz)
The deployment unit of an ArcGIS Explorer add-in is a zip archive with the file extension .eaz, known as an add-in file. An add-in file contains an ArcGIS Explorer Addins.xml file which describes the customizations contained in the file, compiled code and supporting files for the customizations, and also any images used to display buttons on the ArcGIS Explorer Ribbon. One or more customizations may be packaged into a single add-in file. When ArcGIS Explorer needs to load an add-in, it will unpack the contents of the add-in file.
If you want to browse the contents of the .eaz file, you can rename the file to .zip and use Windows Explorer to investigate the contents.
Every add-in file includes a file called AddIns.xml - this is an XML manifest file that describes the customizations in the add-in. See below for an example of an XML manifest file:
[XML]
<?xml version="1.0" encoding="utf-8"?>
<ExplorerAddIns
name="My Explorer AddIns"
description=""
publisher="ESRI"
groupCaption="My Add-Ins">
<button
id="AddInsProject3.Button1"
assembly="AddInsProject3.dll"
className="AddInsProject3.Button1"
caption="My Button"
largeImage="Images\Button1.png"/>
<extension
id="AddInsProject3.Extension1"
assembly="AddInsProject3.dll"
className="AddInsProject3.Extension1"/>
</ExplorerAddIns>
The Visual Studio Tools for ArcGIS Explorer update this file when you create new customizations. You can also directly edit this file if required. For example, you can edit a tooltip and add line breaks in tooltips by specifying 

 in the tooltip string.
Add-In Cache
ArcGIS Explorer looks in a known location under the user profile to load add-ins. By default this location is:
- Windows XP - C:\Documents and Settings\<username>\Application Data\ESRI\ArcGIS Explorer\AddIns
- Windows Vista - C:\Users\<username>\AppData\Roaming\ESRI\ArcGIS Explorer\AddIns
The Visual Studio Tools for ArcGIS Explorer that are used to create new add-in projects contain MSBuild tasks which create the add-in file for automatically when the project is built.
When a new add-in file is found in this location by ArcGIS Explorer, it will unpack the contents of the file into a cache. ArcGIS Explorer will check if any add-ins have been updated in this location on startup, and if necessary unpack the updated files so that the latest version is used.
For more information about the add-in file creation, see the Visual Studio Tools for ArcGIS Explorer topic.