Definition: Filenames, fullnames and filename extensions

The current definition of a filename extension is the part of the filename that follows the last period in the filename. Formally, the filename consists of a fullname, a period, and the filename extension:

<fullname>.<extension>

where <extension> can contain anything but a period. Formally, the regular expression for the period and the <extension> is:

"[.]([^.]*)$"

Possible future changes

We are discussing changing the definition of a filename extension so that it may consist of dots as well, e.g. *.birdseed.data.txt. Note that such a change would by definition also change the content of the fullname. For instance, consider filename:

TCGA-02-0079-01A-01D-0310-01.birdseed.data.txt

Currently this is parsed as:

fullname=TCGA-02-0079-01A-01D-0310-01.birdseed.data  
extension=txt

whereas in the suggested updated this would be parsed as:

fullname=TCGA-02-0079-01A-01D-0310-01  
extension=birdseed.data.txt

if the extension pattern is "[.](birdseed[.]data[.]txt)$".