Add Searching For Hex Digits as a vim til.

vim/searching-for-hex-digits.md

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+# Searching For Hex Digits
+
+If you want to find sequences of hex digits (`A-F`, `a-f` and `0-9`) in a
+search, you can hack together something like:
+
+```
+/[A-Fa-f0-9]\+
+```
+
+This is a bit verbose, though. Vim has a number of built in character
+classes that can be referenced in searches and substitutions. For hex
+digits, there is `\x`. Using this, the search above can be achieved with:
+
+```
+/\x\+
+```
+
+See `:h \x` for more details and other character classes.