Once you have chosen the data, the list of files chosen is stored, along with the associated HK and GTI files, internally to Xselect. All further operations will act on these files.
However, Xselect also has one workspace for product files ( e.g. from the faint or the select event commands). When these are filled by some command, say faint, then Xselect will point to them rather than the original files. However the original file list is not lost, so by clearing the workspace, you get back to your original selection.
It is important to note that there is only one workspace, so if you give two commands that both use the workspace, for example a faint command, and then a select events, the results of the faint command will be used in the select command, but then will be overwritten. If you want to retain these files, then you should do the following:
xsel > faint
xsel > save workspace
xsel > select events
The saved workspace files can be reloaded later, using the read command.
There are also some commands (e.g. 'sisclean')which produce a single product file which is automatically read back into xselect, without losing the originally chosen data. The file that is read back into Xselect is called xsel_in_event.xsl.
In other cases, for instance extract events, a single output file is produced called xsel_out_event.xsl. When you save this, you will be given the option to read it back into Xselect, but this will clear the previous data.