Tagging medleys (files with multiple songs or tunes)

Here I am just looking for feedback or suggestions on the accepted way to name a FLAC file that has multiple tunes or songs on the same track. This is quite common with Celtic recordings and of course in other genre. We find it desirable to tag the TITLE of the track in the following manner because it is easy to read.

TITLE=Tune1 / Tune2 / Tune3

Here the separator is a "/"

The obvious problem is that the forward slash (/) is not a permitted symbol for use in the file's name in a Windows or Macintosh operating system directory.

From your experience, what is the generally-accepted file naming scheme for files like this?

Dennis...aka "d2b"

No.
On the other hand: this is a fine example that filenames are not supposed to be the primary information storage as they have too many limitations in comparison to the tags.
To create valid filenames there is the $validate() function.

Yes, for this case, which is an enumeration of song titles or sub-titles, stored within one physical media file, ... do not use the characters Slash "/" or Backslash "", ... because of their special meaning in the disk-file-system.
Even the character Apostrophe "'" seems not so good to be used as a delimiter.
Probably the character Tilde "~" can be used to visualize the enumeration of sub-titles.

Personally I would apply a single character like Comma "," or Semicolon ";", ...
if needed for readability, then following by a space character.

The enumeration of songtitles can be stored as a multivalue tag-field ...
TITLE=Tune1
TITLE=Tune2
TITLE=Tune3
... and can be displayed as ...
$meta_sep(TITLE,'; ')

But one should note, that the filename, and the entire filepathname, should not be too long, otherwise there may coming up another problems in the filesystem.

Maybe the word "medley" or "compilation" or "sampler" in the filename is enough, to tell about the expectable contents.

DD.20160320.2150.CET

"Generally accepted"? I doubt that there is such a thing.

I replace most illegal Windows file name characters with dashes. The exceptions to this are question marks and double quotes. Question marks are dropped and double quotes are changed to single quotes in the file name. Managing the exceptions requires using the replace$() function instead of Mp3tag's built-in validate() function.

I have an action group that constructs the file name within a temp variable before renaming the file as the last step. This is the action that deals with illegal characters.

Action type: Format value
Field: TEMP
Format string: $replace(%temp%,,-,/,-,:,-,*,-,?,,",'',<,-,>,-,|,-)