// objective: test the \if, \ifnot, \elsif, \else, and \endif commands
// check: indexpage.xml
// config: ENABLED_SECTIONS = GUARD_ENABLED
/** \mainpage
 *  Unconditional (start)
 *  \if GUARD_ENABLED
 *  Enabled (if).
 *    \if (!GUARD_ENABLED)  Disabled (if).\else Enabled (else). \endif
 *  \else
 *  Disabled.
 *  \endif
 *  Unconditional (middle)
 *  \ifnot GUARD_ENABLED
 *  Disabled (ifnot).
 *  \elseif GUARD_DISABLED
 *  Disabled (elseif).
 *  \else
 *  Enabled (else).
 *  \endif
 *  Unconditional (end)
 */