Anyways, here is the PR: https://github.com/triplea-game/triplea/pull/4140

This has no impact on existing maps that don't use the new parameters. But allows maps to require airbase for interception just like scrambling. It also allows specifying the max number each airbase can send to intercept (default is infinite).

I tested it by editing TWW to have fighters require airfields to intercept and have a limit of 1. Here is the XML examples:

Airfield

    <attachment name="unitAttachment" attachTo="britishAirfield" javaClass="games.strategy.triplea.attachments.UnitAttachment" type="unitType">
      <option name="isAirBase" value="true"/>
      <option name="maxInterceptCount" value="1"/>

Fighter

    <attachment name="unitAttachment" attachTo="britishFighter" javaClass="games.strategy.triplea.attachments.UnitAttachment" type="unitType">
      <option name="canIntercept" value="true"/>
      <option name="requiresAirbaseToIntercept" value="true"/>

<option name="isAirBase" value="true"/>

<option name="maxinterceptCount" value="2"/>

@Hepps Yeah, I think option 3 probably is best since we already have the concept of airbase.

@hepps Yeah, this should be doable in a similar way that scramble works. I'll just need to make sure to keep the existing functionality as well for maps that are already using it. Most likely either add additional parameters to canIntercept, a new unit property requiresUnitToIntercept, or property to require airbase.

Options:
1.
<option name="canIntercept" value="true:germanAirfield:italianAirfield:japaneseAirfield"/>

<option name="canIntercept" value="true"/>
<option name="requiresUnitsToIntercept" value="germanAirfield:italianAirfield:japaneseAirfield"/>

<option name="canIntercept" value="true"/>
<option name="requiresAirbaseToIntercept" value="true"/>

Option 3 seems like it would work best. Since you could make it (as with so many other properties) so that if it was not defined in the XML it would automatically default to "false" in all games. Thereby not affecting any existing game.

<option name="canIntercept" value="true"/>
<option name="requiresUnitsToIntercept" value="germanAirfield:italianAirfield:japaneseAirfield"/>

This just happens so many times in mapmaking. You have to manually list all units that you know are all "things that obviously enable intercepting". The same happens when e.g. you have to keep listing all units that can accept a particular support, or units that can be targeted by a particular AA attack, etc. It would make things a hell a lot easier if we had macros, or definable unit / territory / etc. categories. Something like

<categories>
    <category name="enableIntercept" type="unit">
        <element name="germanAirfield"/>
        <element name="italianAirfield"/>
        <element name="japaneseAirfield"/>
    </category>
    
    <category name="isAffectedByMyFavouriteTrigger" type="unit">
        <element name="aLongListOfUnits"/>
        <element name="evenMoreUnits"/>
        <element name="youDontHaveToModifyAMillionTriggers"/>
        <element name="whenYouChangeAroundStuff"/>
        <element name="youOnlyHaveToModifyThisCategory"/>
    </category>
</categories>

and then

<option name="canIntercept" value="true"/>
<option name="requiresUnitsToIntercept" value="enableIntercept"/>

and

<attachment name="triggerAttachment_myFavouriteTrigger_No_13618567561" attachTo="Japanese" javaClass="games.strategy.triplea.attachments.TriggerAttachment" type="player">
	<option name="conditions" value="conditionAttachment_myFavouriteCondition_No_13618567561"/>
	<option name="unitType" value="isAffectedByMyFavouriteTrigger"/>
	<option name="unitProperty" value="attack" count="1"/>
	<option name="uses" value="1"/>
</attachment>

And if you decide that in the next version the unit evenMoreUnits is no longer worthy of being affected by all of the million triggers, you simply delete one line, instead of deleting one line from each trigger.

Options:
1.

<option name="canIntercept" value="true:germanAirfield:italianAirfield:japaneseAirfield"/>

<option name="canIntercept" value="true"/>
<option name="requiresUnitsToIntercept" value="germanAirfield:italianAirfield:japaneseAirfield"/>

<option name="canIntercept" value="true"/>
<option name="requiresAirbaseToIntercept" value="true"/>

I shall think on it though.

This might be overreaching but would be cool if the airfield could use the "requires units" thingy so planes could get + or - bonuses.

I remember trying to have bombers get +2 on their sbr raids but only if they left from a airfield. Wasn't able to do it though.

Anyway, not to sidetrack things too much : )