For each word in a dictionary, all possible combinations of upper- and lower-case variants are generated.

In hashcat-legacy, this attack was implemented as a stand-alone attack mode. In hashcat there are two ways to do it.

With a table. The Table attack (-a 5) ships a case table, and this is the closest thing to the old stand-alone mode:

$ hashcat -m 0 -a 5 hash.txt words.txt tables/toggle.table

tables/toggle.table covers 618 characters in both directions, including Greek and Cyrillic, and each letter is decided separately.

With rules. The other way is a ruleset, described in Using rules to emulate toggle attack.

If our dictionary contains the word

pass1234

Hashcat creates the following password candidates

pass1234
Pass1234
pAss1234
PAss1234
paSs1234
PaSs1234
pASs1234
PASs1234
pasS1234
PasS1234
pAsS1234
PAsS1234
paSS1234
PaSS1234
pASS1234
PASS1234