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?