Allow past/future in ExprLevel via default value

[sovdeeth]

Problem

ExprLevel supported past/future values if the default player was used. However, the pattern did not allow the default player, preventing the use of past/future values.

Solution

Used registerDefault instead of register. Improved code quality, added example, added an extra check for changing past/future values in a level change event.

Testing Completed

Manual testing confirmed.

on level change:
    set {_diff} to future xp level - past exp level
    broadcast "%player%'s level changed by %{_diff}%!"

Supporting Information

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Completes: none
Related: none