G'day Rolf,

Purely for readability, I generally try to keep the modifiers in alphabetical order. In that respect, I concur with ++hippo's response.

I'm pretty sure that the "xms default" came about, because that was the order they were introduced in the book "Perl Best Practices".

1. Always use the /x flag. (pp. 236-237)
2. Always use the /m flag. (pp. 237-239)
3. Always use the /s flag. (pp. 240-241)

Some modifiers can be applied to the regex itself (e.g. /x); others, to any operation the regex is involved in (e.g. /g); and others to only a specific operation (e.g. /e). It's a fatal error to use them in the wrong places:

$ perl -E 'say qr{}x'
(?^ux:)
$ perl -E 'say qr{}g'
Unknown regexp modifier "/g" at -e line 1, near "say "
Execution of -e aborted due to compilation errors.
$ perl -E 'say m{}g'

$ perl -E 'say m{}e'
Unknown regexp modifier "/e" at -e line 1, near "say "
Execution of -e aborted due to compilation errors.
$ perl -E 'say s{}{}e'
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I can see some benefit in keeping those grouped together: your initial example of xegis would become isxge.

I'm also not averse to ++AnomalousMonk's suggestion of using a separator. In which case, xegis would become isx_g_e.

Overall, I'm not too bothered by personal preferences regarding modifier ordering: deciding upon a single style, and using it consistently, is far more important, in my opinion.