I’m kinda struggling with a supposedly pretty simple task:
I have two regex like these:

[A-Z0-9 /=-–!"#$().?@[]´/+=§°½¾ÄÖßÜ品纺]{1,18} and ^[^0s][A-Z0-9_//=.-]{1,17}$

Now I need to make sure, that the _-sign can’t be there back to back. I know that it should work with ? to match 0 and 1 times, but I think I’m struggling with the capture group here.

To make it more understandable:

DF_TEST_123480        // valid
DF_TEST__312804=1234  // not valid
DF__TEST_312804=1234  // not valid
DF__TEST__312804=1234 // not valid

Is there an easy way to adjust this? I also tried using {0,1} but as I said, I think because it is the capture group, it isn’t doing exactly what I’m looking for.