I was playing around with Bash variables and mistakenly used the -c option (for const) to declare instead of the correct -r option to create a readonly variable. To my surprise, the variable retained the -c attribute and capitalized the first letter of whatever value I assigned.
This behavior is not listed in declare's usage, either within the declare --help output or on Bash's info page. It seems to be incompatible with ksh's typeset, though the -u and -l options are compatible.
Is this a well-known undocumented feature? Is it generally available?
declare -c, -l, and -u appear to have been added all together in bash 4.0 (introduced in 4.0-rc1), as long as the --enable-casemod-attributes configure flag isn't disabled (it's enabled by default). There are tests for them (in tests/casemod.tests). Why -c was never documented is a mystery.