-footer option is "downgraded" to a no-op, with a warning if it is used.
The underlying problem was initially reported as an accessibility issue (ambiguous elements), but instead of solving the problem by naming the two navbar elements, the solution is to stop generating the lower navbar: it serves no useful purpose, since the upper one is always displayed at the top of the browser window.
The side-effect of this is that the
-footer option (used to optionally inject user-specified text into the lower navbar) is now redundant. There is little evidence the option was often used, since it defaulted to the value of the
-header option, used to optionally inject text into the upper navbar.
The option is retained, for now, but is effectively a no-op.
A warning is given if the option is used, including a warning that the option may be removed in a future release.