PatchOperations are a feature that allows you to modify the content of XML Defs. Prior to RimWorld alpha 17, modders could only modify Defs by creating new ones that overwrote the original; this often resulted in compatibility issues as if more than one mod tried to overwrite the same Def, only the last mod in the load order would succeed as prior ones would themselves be overwritten.

Basics

PatchOperations are written as XML nodes that go into your mod's Patches folder:

MyModFolder
├ About
├ Defs
└ Patches
  └ MyPatchFile.xml

Just as with XML Defs, folder and file names do not matter and you can freely name and organize your patche files in whatever manner you wish. Individual patches themselves are a standard XML file with <Patch> as the root tag:

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

  <!-- PatchOperations go here -->

</Patch>

XPath

Most PatchOperations must be targeted at one or more XML nodes inside the master XML document. This is done via XML Patch Language or XPath.

Note that an XPath is targeting the structure of the XML document after it's been parsed by RimWorld's parser, thus it has nothing to do with the actual file or folder paths. For example, if you wanted to add a stat value to the vanilla Wall building, you might use an XPath like so:

Defs/ThingDef[defName="Wall"]/statBases

The first segment of any XPath targeting an XML Def will be Defs/ as all XML Defs use the <Defs> root tag.
The square brackets denote a predicate, or conditional match. In this case, we are looking for ThingDefs that have a child tag defName equal to "Wall".

You can target Defs that do not have a defName (such as abstract bases) by targeting their identifying attributes. For example, if you wanted to add another Stuff category to the abstract base Def for all shelves, you might use the following xpath:

Defs/ThingDef[@Name="ShelfBase"]/stuffCategories

Additional XPath resources:

PatchOperation Types

Basic XML node operations:

PatchOperationAdd adds a provided child node to the selected node
PatchOperationInsert inserts a provided sibling node above the selected node
PatchOperationRemove deletes the selected node
PatchOperationReplace replaces the selected node with the provided node

XML attribute operations:

PatchOperationAttributeAdd adds a provided attribute to the selected node if and only if the attribute name is not already present
PatchOperationAttributeSet sets a provided attribute for the selected node, overwriting the attribute value if the attribute name is already present
PatchOperationAttributeRemove removes an attribute for the selected node

Special operations:

PatchOperationSequence contains a set of other PatchOperations, and aborts upon any operation failing
PatchOperationAddModExtension adds a ModExtension.
PatchOperationSetName changes the name of a node.

Conditional operations:

PatchOperationFindMod tests for the presence of another mod, and can do different operations depending on the result.
PatchOperationConditional tests nodes, and can do different operations depending on the result.
PatchOperationTest tests nodes, which is useful inside a PatchOperationSequence

PatchOperationAdd

Inserts the specified values as a child node of the XML nodes targeted by the operation's xpath. By default, the new nodes will be inserted after (appended to) any existing child nodes. You can use <order>Prepend</order> in the patch operation (order is Append by default).

Note: PatchOperationAdd will not overwrite any existing tags. If one of your values overlaps with an existing node and you are not targeting a list node, then it will cause an error on game load.

Before

Patch operation

After

<ExampleDef>
  <defName>SampleDef</defName>
  <aaa>Some text</aaa>
</ExampleDef>

<Operation Class="PatchOperationAdd">
  <xpath>Defs/ExampleDef[defName="SampleDef"]</xpath>
  <value>
    <bbb>New text</bbb>
  </value>
</Operation>

<ExampleDef>
  <defName>SampleDef</defName>
  <aaa>Some text</aaa>
  <bbb>New text</bbb>
</ExampleDef>

<ExampleDef>
  <defName>SampleDef</defName>
  <exampleList>
    <li>Bar</li>
  </exampleList>
</ExampleDef>

<Operation Class="PatchOperationAdd">
  <xpath>Defs/ExampleDef[defName="SampleDef"]/exampleList</xpath>
  <order>Prepend</order>
  <value>
    <li>Foo</li>
  </value>
</Operation>

<ExampleDef>
  <defName>SampleDef</defName>
  <exampleList>
    <li>Foo</li>
    <li>Bar</li>
  </exampleList>
</ExampleDef>

PatchOperationInsert

Inserts the specified values as a sibling above the selected node(s). You can specify <order>Append</order> to insert it after the targeted node(s) instead (default is Prepend).

Before

Patch operation

After

<ExampleDef>
  <defName>Rainbow</defName>
  <colors>
    <li>Red</li>
    <li>Yellow</li>
    <li>Green</li>
    <li>Blue</li>
    <li>Violet</li>
  </colors>
</ExampleDef>

<Operation Class="PatchOperationInsert">
  <xpath>Defs/ExampleDef[defName="Rainbow"]/colors/li[text()="Yellow"]</xpath>
  <value>
    <li>Orange</li>
  </value>
</Operation>

<ExampleDef>
  <defName>Rainbow</defName>
  <colors>
    <li>Red</li>
    <li>Orange</li>
    <li>Yellow</li>
    <li>Green</li>
    <li>Blue</li>
    <li>Violet</li>
  </colors>
</ExampleDef>

<ExampleDef>
  <defName>Fish</defName>
  <lines>
    <li>one fish</li>
    <li>two fish</li>
  </lines>
</ExampleDef>

<Operation Class="PatchOperationInsert">
  <xpath>Defs/ExampleDef[defName="Fish"]/lines/li[text()="two fish"]</xpath>
  <order>Append</order>
  <value>
    <li>red fish</li>
    <li>blue fish</li>
  </value>
</Operation>

<ExampleDef>
  <defName>Fish</defName>
  <lines>
    <li>one fish</li>
    <li>two fish</li>
    <li>red fish</li>
    <li>blue fish</li>
  </lines>
</ExampleDef>

PatchOperationRemove

Removes the targeted node.

Before

Patch operation

After

<ExampleDef>
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
</ExampleDef>

<Operation Class="PatchOperationRemove">
  <xpath>Defs/ExampleDef[defName="Sample"]/bar</xpath>
</Operation>

<ExampleDef>
  <defName>Sample</defName>
  <foo>Uno</foo>
  <baz>Tres</baz>
</ExampleDef>

PatchOperationReplace

Replaces the selected node(s) with your values.

Before

Patch operation

After

<ExampleDef>
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
</ExampleDef>

<Operation Class="PatchOperationReplace">
  <xpath>Defs/ExampleDef[defName="Sample"]/baz</xpath>
  <value>
    <baz>Drei</baz>
  </value>
</Operation>

<ExampleDef>
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Drei</baz>
</ExampleDef>

PatchOperationAttributeAdd

Adds the specified attribute to the targeted node(s), but only if that attribute is not yet present.

Before

Patch operation

After

<ExampleDef>
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
</ExampleDef>

<Operation Class="PatchOperationAttributeAdd">
  <xpath>Defs/ExampleDef[defName="Sample"]</xpath>
  <attribute>Name</attribute>
  <value>SampleBase</value>
</Operation>

<ExampleDef Name="SampleBase">
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
</ExampleDef>

PatchOperationAttributeSet

Adds the specified attribute to the targeted node(s), or overwrites the existing value if the specified attribute already exists.

Before

Patch operation

After

<ExampleDef Name="SampleSource">
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
</ExampleDef>

<Operation Class="PatchOperationAttributeSet">
  <xpath>Defs/ExampleDef[defName="Sample"]</xpath>
  <attribute>Name</attribute>
  <value>SampleBase</value>
</Operation>

<ExampleDef Name="SampleBase">
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
</ExampleDef>

PatchOperationAttributeRemove

Removes the specified attribute from the targeted node(s).

Before

Patch operation

After

<ExampleDef Name="SampleBase">
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
</ExampleDef>

<Operation Class="PatchOperationAttributeRemove">
  <xpath>Defs/ExampleDef[defName="Sample"]</xpath>
  <attribute>Name</attribute>
</Operation>

<ExampleDef>
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
</ExampleDef>

PatchOperationAddModExtension

Main article: Modding Tutorials/DefModExtension

Adds the specified DefModExtension to the targeted Def. Automatically creates a <modExtensions> node if one doesn't already exist.

Before

Patch operation

After

<ExampleDef Name="SampleBase">
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
</ExampleDef>

<Operation Class="PatchOperationAddModExtension">
  <xpath>Defs/ExampleDef[defName="Sample"]</xpath>
  <value>
    <li Class="MyNamespace.MyModExtension">
      <key>Value</exampleValue>
    </li>
  </value>
</Operation>

<ExampleDef Name="SampleBase">
  <defName>Sample</defName>
  <foo>Uno</foo>
  <bar>Dos</bar>
  <baz>Tres</baz>
  <modExtensions>
    <li Class="MyNamespace.MyModExtension">
      <key>Value</exampleValue>
    </li>
  </modExtensions>
</ExampleDef>

PatchOperationSetName

Changes the name of a node. Most useful for changing the names of the nodes in "dictionary"-style nodes without changing their contents, such as for stat blocks or recipe products.

Before

Patch operation

After

<ThingDef>
  <defName>ExampleThing</defName>
  <!-- many nodes omitted -->
  <statBases>
    <Insulation_Cold>10</Insulation_Cold>
  </statBases>
</ThingDef>

<Operation Class="PatchOperationSetName">
  <xpath>Defs/ThingDef[defName="ExampleThing"]/statBases/Insulation_Cold</xpath>
  <name>Insulation_Heat</name>
</Operation>

<ThingDef>
  <defName>ExampleRecipe</defName>
  <!-- many nodes omitted -->
  <statBases>
    <Insulation_Heat>10</Insulation_Heat>
  </statBases>
</ThingDef>

<RecipeDef>
  <defName>ExampleRecipe</defName>
  <!-- many nodes omitted -->
  <products>
    <WoodLog>30</WoodLog>
  </products>
</RecipeDef>

<Operation Class="PatchOperationSetName">
  <xpath>Defs/RecipeDef[defName="ExampleRecipe"]/products/WoodLog</xpath>
  <name>Steel</name>
</Operation>

<RecipeDef>
  <defName>ExampleRecipe</defName>
  <!-- many nodes omitted -->
  <products>
    <Steel>30</Steel>
  </products>
</RecipeDef>

PatchOperationSequence

Contains one or more additional PatchOperations, which are executed in order. If any of them fail, then the Sequence stops and will not run any additional PatchOperations.

WARNING: PatchOperations within an XML file will run in order even without a PatchOperationSequence and using a PatchOperationSequence can obfuscate or hide errors, making it difficult to debug if your child PatchOperations have errors. Do not use PatchOperationSequence unless you are sequencing multiple PatchOperations with a single PatchOperationConditional or PatchOperationFindMod or you are using MayRequire on child PatchOperations, and even then it's strongly recommended you write your PatchOperations as independent Operations first to ensure they are working as intended.

<Operation Class="PatchOperationSequence">
  <operations>
    <li Class="PatchOperationAdd">
      <xpath>Defs/ExampleDef[defName="Sample"]/statBases</xpath>
      <value>
        <Mass>10</Mass>
      </value>
    </li>
    <li Class="PatchOperationSetName">
      <xpath>Defs/ExampleDef[defName="Sample"]/statBases/Flammability</xpath>
      <name>ToxicEnvironmentResistance</name>
    </li>
    <!-- etc -->
  </operations>
</Operation>

As mentioned, you can use Template:Modding Tutorials/MayRequire on child operations of a PatchOperationSequence, but you should test them individually before adding them to said Sequence:

<Operation Class="PatchOperationSequence">
  <operations>
    <li Class="PatchOperationAdd" MayRequire="Ludeon.Rimworld.Biotech"> <!-- Only runs if Biotech is active -->
      <xpath>Defs/ThingDef[defName="MechGestator"]/recipes<xpath>
      <value>
        <li>MyCustomMech</li>
      </value>
    </li>
    <li Class="PatchOperationAdd" MayRequire="MyProject.OtherModPackageId"><!-- Only runs if the specific mod is active -->
      <xpath>Defs/ThingDef[defName="OtherModWorkbench"]/recipes</xpath>
      <value>
        <li>MyCustomResource</li>
      </value>
    </li>
  </operations>
</Operation>

PatchOperationFindMod

Checks whether any of the specified mods or DLCs are loaded and allows you to run an additional PatchOperation for match or nomatch results.

WARNING: Unlike all other mod-compatibility features in RimWorld, PatchOperationFindMod uses the mod name and not its packageId.

The following example adds a mod extension to the targeted Defs if RimQuest is loaded (See original):

<Operation Class="PatchOperationFindMod">
  <mods>
    <li>RimQuest</li>
  </mods>
  <match Class="PatchOperationAddModExtension">
    <xpath>Defs/IncidentDef[defName="MFI_DiplomaticMarriage" or defName="MFI_HuntersLodge" or defName="MFI_Quest_PeaceTalks"]</xpath>
    <value>
      <li Class = "RimQuest.RimQuest_ModExtension">
        <canBeARimQuest>false</canBeARimQuest>
      </li>
    </value>
  </match>
</Operation>

The following example replaces the tabWindowClass of the Factions button when Relations Tab is not loaded:

<Operation Class="PatchOperationFindMod">
  <mods>
    <li>Relations Tab</li>
  </mods>
  <nomatch Class="PatchOperationReplace">
    <xpath>/Defs/MainButtonDef[defName="Factions"]/tabWindowClass</xpath>
    <value>
      <tabWindowClass>MyNameSpace.MyTabWindowClass</tabWindowClass>
    </value>
  </nomatch>
</Operation>

PatchOperationConditional

Tests for the existence/validity of the specified node(s) and allows you to run optional match or nomatch PatchOperations in response.

The following example adds a <comps> node to the Caravan Def if it does not exist already, then adds a custom comp to said list:

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

  <!-- add comps field to Caravan WorldObjectDef if it doesn't exist -->
  <Operation Class="PatchOperationConditional">
    <xpath>Defs/WorldObjectDef[defName="Caravan"]/comps</xpath>
    <nomatch Class="PatchOperationAdd">
      <xpath>Defs/WorldObjectDef[defName="Caravan"]</xpath>
      <value>
        <comps />
      </value>
    </nomatch>
  </Operation>

  <!-- add pyromaniac caravan handler comp to Caravan WorldObjectDef -->
  <Operation Class="PatchOperationAdd">
    <xpath>Defs/WorldObjectDef[defName="Caravan"]/comps</xpath>
    <value>
      <li Class="BetterPyromania.WorldObjectCompProperties_Pyromania">
        <fuelCount>20</fuelCount>
        <cooldown>30000</cooldown>
        <needThreshold>0.5</needThreshold>
      </li>
    </value>
  </Operation>

</Patch>

PatchOperationTest

!

Obsolete

The following content was written for a previous version of RimWorld or is otherwise no longer fully relevant today. Please be mindful of any potential inaccuracies.

Tests for the existence/validity of an xpath. Useful as a way to intentionally stop a PatchOperationSequence.

NOTE: Conditionally applying patches in this way is considered obsolete. Using PatchOperationConditional is a much better idea as the use of <success>Always</success> here will also suppress legitimate errors, making Sequences difficult to debug.

The following example patch is from Apparello, by Shinzy.

<Operation Class="PatchOperationSequence">
  <!-- Must use <success>Always</success> because of the PatchOperationTest -->
  <success>Always</success>
  <!-- check for worn graphics and if none found, add one -->
  <operations>
    <li Class="PatchOperationTest">
      <xpath>Defs/ThingDef[defName = "Apparel_Pants"]/apparel/wornGraphicPath</xpath>
      <success>Invert</success>
    </li>
    <li Class="PatchOperationAdd">
      <xpath>Defs/ThingDef[defName = "Apparel_Pants"]/apparel</xpath>
      <value>
        <wornGraphicPath>Accessorello/Pants/Pants</wornGraphicPath>
      </value>
    </li>
  </operations>
</Operation>

Miscellaneous

Custom PatchOperations

Custom PatchOperation types can be created in C# by subclassing Verse.PatchOperation, which is useful for performing a patch based on ModSettings values or other custom behavior.

A tutorial for this process does not exist yet, but you can check out the following references of custom PatchOperations: 9 XML Extensions - An entire framework mod containing many useful custom PatchOperations. - PatchOperationMakeGunCECompatible - Used by Combat Extended to automatically apply multiple changes to a single firearm for compatibility. - PatchOperationAddOrReplace - An example of a custom variant of PatchOperationAdd that replaces an existing value.

"Success" Option

!

Obsolete

The following content was written for a previous version of RimWorld or is otherwise no longer fully relevant today. Please be mindful of any potential inaccuracies.

The <success>...</success> node determines how errors are handled, usually in a PatchOperationSequence. Note that use of this tag should be considered obsolete; its use was common before PatchOperationConditional was implemented, but it should no longer be required and can cause confusion as it can suppress legitimate errors from showing up.

Options available are:

Always - This patch operation always succeeds, i.e. it suppresses all errors that might have occurred. This used to be used in PatchOperationSequence along with PatchOperationTest in order to conditionally run patches, but is now obsolete.
Normal - Errors are handled normally
Invert - Errors are considered a success and success is considered a failure. This used to be used in PatchOperationSequences to test the negative of a PatchOperationTest; you should now use <nomatch> on PatchOperationConditional
Never - This patch operation always fails. Generally only used in testing to see if a Sequence is working correctly, should never be used in published mods.

Tips and Tricks

Patching is run after all XML Defs are loaded into memory and in mod list order. If you are encountering compatibility issues with another mod's PatchOperations, you can use loadBefore and loadAfter in your About.xml to help players resolve these issues.
Patching is done before Def inheritance takes place. This means that you cannot target tags that are inherited from a parent, but also that if you alter a parent, all of its children will inherit the patched value.
You can override a value inherited from a parent Def without changing that value for all Defs by using Inherit="False":

<Operation Class="PatchOperationAdd">
  <xpath>/Defs/ThingDef[defName = "Apparel_KidPants"]</xpath>
  <value>
    <thingCategories Inherit="False">
      <li>NewValue</li>
    </thingCategories>
  </value>
</Operation>

You can use or in predicates to target multiple nodes: Defs/ThingDef[defName="Cassowary" or defName = "Emu" or defName = "Ostrich" or defName = "Turkey"] This is generally better than using multiple PatchOperations so long as you are making the same changes to each target.
You can use /text() to target the text contents of a tag instead of the whole tag for operations like PatchOperationReplace. This is especially useful if you do not want to accidentally remove attributes.

Common Issues / Troubleshooting

XPath and XML nodes in general is case-sensitive and must be exact. Copying values such as defName fields is strongly recommended to avoid errors.
Malformed XML such as unclosed or mismatched tags can cause the XML parser to crash completely, which can result in a blank screen on startup or a "Recovered from a fatal error" screen and the removal of all active mods. If this occurs, run all of your XML through an XML validator to ensure that it is structurally correct. Checking your Player.log file can help in diagnosing the exact cause as well.
It's very easy to confuse Insert vs Add; Insert will "add" the value as a sibling of the target node(s), while Add will "insert" the value as a child of the target node(s).
Remember that XPath targets the XML data structure, not the file path.
If you're still stumped, feel free to join the RimWorld Discord server and ask questions in the #mod-development channel.

References and Links

!

Obsolete

The following content was written for a previous version of RimWorld or is otherwise no longer fully relevant today. Please be mindful of any potential inaccuracies.

The best tutorial on PatchOperations created by Zhentar: Introduction to PatchOperation

Modding Tutorials/PatchOperations

Contents

Basics

XPath

PatchOperation Types

PatchOperationAdd

PatchOperationInsert

PatchOperationRemove

PatchOperationReplace

PatchOperationAttributeAdd

PatchOperationAttributeSet

PatchOperationAttributeRemove

PatchOperationAddModExtension

PatchOperationSetName

PatchOperationSequence

PatchOperationFindMod

PatchOperationConditional

PatchOperationTest

Miscellaneous

Custom PatchOperations

"Success" Option

Tips and Tricks

Common Issues / Troubleshooting

References and Links

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