How can I make an exception for Item Slots?

[Lawful_g]

Some things are groups that can be worn together in the same item slot at the same time. Chronocharms, for example, can have any number in the neck slot. Also, you can wear 2 Mind Blade Gauntlets in the Hands slot at the same time.

How do I prevent an error from appearing when multiples are being equipped?

[Lawful_g]

Or how would I make a ring take up both ring slots, for another example?

[chiefweasel]

Lawful_g, you will also run into a problem that I did when trying to add items from the MIC. The MIC re-created the slots available for gear. Its different from the one used in the 3.5 books. the HL product uses the HL book and not the MIC. So you will run into problems trying to do a 1 to 1 comparison between them.

[Lawful_g]

I noticed that the names for the slots are different, but I don't see any substantive differences.

For example, the MIC has Face as a slot, but HL calls it Eyes. Arms = Wrist, Chest = Torso, Body = Armor

[Lawful_g]

And other than this issue with the slots I am done with the clothing section now.

[Mathias]

hero.assign[Hero.EqpRing] will use up a ring slot on the character. hero.assign[ExtraSlot.EqpRing] will add a ring slot, so you can have your items that don't use up a slot add that tag once they're equipped.

The tags are (take what's listed as the id for each of these tags, and put it in the Hero or ExtraSlot tag groups):

 
    <value id="EqpTorso" name="Chest"/>     <!-- Torso equipment slot used (e.g. Vest, vestments, shirt) -->
    <value id="EqpArmor" name="Armor"/>     <!-- Armor equipment slot used (e.g. Armor, robes) -->
    <value id="EqpWaist" name="Waist"/>     <!-- Waist equipment slot used (e.g. Belt) -->
    <value id="EqpBack" name="Back"/>       <!-- Back equipment slot used (e.g. Cloak, cape, mantle) -->
    <value id="EqpWrist" name="Wrist"/>     <!-- Wrist equipment slot used (e.g. Bracelets, bracers) -->
    <value id="EqpRing" name="Ring"/>       <!-- Ring (max 2!) equipment slot used -->
    <value id="EqpHand" name="Hand"/>       <!-- Hand equipment slot used (e.g. Gloves, gauntlets) -->
    <value id="EqpFoot" name="Foot"/>       <!-- Foot equipment slot used (e.g. Boots, shoes) -->
    <value id="EqpPFRune" name="Rune (Pathfinder)"/>   <!-- Rune equipment slot used (e.g. Runes from Pathfinder) -->

They're checked at Validation/10000, so you're not really restricted on your timing.