[seq] Scentific notation

[Dmitry Bogatov]

Hello! I found in seq.c:152 following line:

    if (! arg[strcspn (arg, "xX")] && isfinite (ret.value))

where arg is checked to be valid double (check for `xstrtold'
success) just before. I checked for `git blame`, it refers to
86e4b778, and commit message talk about scentific notation.

Can you point me to documention about "xX" symbols in double?
I found only about "1e-6" -- like style.

-- 
Best regards, Dmitry Bogatov <address@hidden>,
     GNU Thales maintainer and netiquette guardian.
GPG: D1E0591E0037BDCCBEE56002788BE01254B7F00D