When did the colon character : become an allowed character in the filesystem? Just noticed it works on Maverick.. the colon character : is valid for file and directory names (I accidentally entered it for a filename in Atom).

Can't find any reference to it becoming valid though (http://en.wikipedia.org/wiki/Hierarchical_File_System still marks it as invalid).

It works in the Atom editor.

I can create a file called : with nano.

This works echo 'test' &gt; : &amp;&amp; cat :

In TextWrangler it only works if the file already exists but won't create it (with command line tools installed edit :)

Is this new from Mavericks? Works in Yosemite? Before?

Edit: A few more tests: 


TextEdit won't allow me to enter it and always replace it with -
Finder won't allow me to create a folder with the name :

A : file created via command line is displayed as / in Finder.. and double clicking it will open it in TextEdit. TextEdit will load its content but show the name / in the title bar.
This change appeared at the beginning of MacOS X (i.e. MacOS X 10).

Then the directory separator from HFS :
was changed to the directory separator of UFS /. Since then the Finder is in charge of making the following mapping:

/ → :
: → /