A17; changes

[AngleWyrm]

XPath and XPointer on O'Reilly Commons Downloadable PDF

[SihvMan]

Something to note, having made a half dozen patches recently. This might be a "no duh" for some, but I'll include it for completeness' sake.

When patching using the <Patch> method, you cannot patch to an Base/Abstract. The way RimWorld loads mods makes it load Abstract->Def->Patch, such that the inheritors receive the un-patched abstract.

That being said, you can patch Defs that have inherited abstracts, as though the stuff in the abstract is actually in the inheritor's Def. Ex: If the abstract has <comps>, but the inheritor does not, a patch's <xpath> can be

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<xpath>//ThingDef[defName = "InheritorDef"]/comps</xpath>
but not

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<xpath>//ThingDef[defName = "AbstractDef"]/comps</xpath>

Also, when patching to <comps> you can patch to specific comps with

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<xpath>//ThingDef[defName = "ExampleDef"]/comps/li[@Class="CompProperties_ExampleProperty"]</xpath>

This can used in the place of li(#) if you're patching multiple things with similar comps, in case the comp being patched is in multiple Defs at different list #'s (fringe case, but was useful when I made the patch for Anonemous2's MoreFurniture).

[NoImageAvailable]

When patching using the <Patch> method, you cannot patch to an Base/Abstract. The way RimWorld loads mods makes it load Abstract->Def->Patch, such that the inheritors receive the un-patched abstract.

Just did a test mod and this is not the case as of 0.17.1543. For reference, the patch I used was:

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<?xml version="1.0" encoding="utf-8" ?>
<Patch>

<Operation Class="PatchOperationReplace">
  <xpath>//DamageDef[@Name = "LocalInjuryBase"]/workerClass</xpath>
  <value>
    <workerClass>DamageWorker_Flame</workerClass>
  </value>
</Operation>

</Patch>

The change carried through to all child defs.

From what I've been told the under-the-hood process is XML files are loaded into memory, patches are applied and then the XML parser interprets things like abstracts into actual game objects.

Edit: Another thing you can do with def inheritance is use PatchOperationAddAttribute to add a Name to a vanilla def, then have your own defs inherit from it. I imagine you could also use that method to mess around with inheritance of vanilla defs to change their base defs and such (didn't test this one though).