What format does Xcode use to display 'data' types in plist files? If I open a .plist file in TextEdit, all the properties with type "data" are displayed in Base64 encoding, for example
&lt;data&gt;SGFja2ludG9zaA==&lt;/data&gt;.

Xcode shows these values in some other format, like
&lt;54657374 56616c75 65&gt;.  What is this format called, and how can I convert it to ASCII?
The data is just a hex dump of the decoded base64 encoding. To convert to ASCII, look the hex values up in the ASCII table. For your example:

54657374 56616c75 65


is

TestValue


A convenient way to get the table is man ascii from a terminal prompt.