Using LEAP42.1 with KDE Plasma desktop.

I wish to understand how is the sort order for displaying files in Dolphin determined.
I ask because I have a list of 50+ files which include in their file name "[Disk_X]" where X is 1 to 56.
Even with leading zeros missing they still display in correct order in Dolphin

However when I look at same directory with Puddletag I get a different order with files with single digit numbers shown at end of decade eg: [Disk_1] follows [Disk_19]. [Disk_2] follows [Disk_29] etc.

I have solved the problem by including leading zeros but am interested to learn what determines the sort order in each case.