Operators

• = late evaluation (expand variable when used)
• := immediately expand
• += append (with space)
• =+ prepend (with space)
• .= append (without space)
• =. prepend (without space)
• ?= assign if no other value was assigned
• ??= assign if no other value was assigned (lower priority than mentioned above)

Rethink usage of += and similar in local.conf. Example:

• If += is parsed before ?=, the latter will be omitted.
• Solution: use _append to unconditionally appends a value.