Move extensionDefinitionPrefix to YamlConfiguration.

src/main/kotlin/com/charleskorn/kaml/Yaml.kt

@@ -30,13 +30,12 @@ import org.snakeyaml.engine.v1.api.StreamDataWriter
 import java.io.StringWriter
 
 class Yaml(
-    val extensionDefinitionPrefix: String? = null,
     override val context: SerialModule = EmptyModule,
     val configuration: YamlConfiguration = YamlConfiguration()
 ) : AbstractSerialFormat(context), StringFormat {
     override fun <T> parse(deserializer: DeserializationStrategy<T>, string: String): T {
         val parser = YamlParser(string)
-        val reader = YamlNodeReader(parser, extensionDefinitionPrefix)
+        val reader = YamlNodeReader(parser, configuration.extensionDefinitionPrefix)
         val rootNode = reader.read()
         parser.ensureEndOfStreamReached()
 

src/main/kotlin/com/charleskorn/kaml/YamlConfiguration.kt

@@ -23,8 +23,10 @@ package com.charleskorn.kaml
  *
  * [encodeDefaults]: set to false to not write default property values to YAML (defaults to true)
  * [strictMode]: set to true to throw an exception when reading an object that has an unknown property, or false to ignore unknown properties (defaults to true)
+ * [extensionDefinitionPrefix]: prefix used on root-level keys (where document root is an object) to define extensions that can later be merged (defaults to null, which disables extensions altogether). See https://batect.charleskorn.com/config/Overview.html#anchors-aliases-extensions-and-merging for example.
  */
 data class YamlConfiguration constructor(
     internal val encodeDefaults: Boolean = true,
-    internal val strictMode: Boolean = true
+    internal val strictMode: Boolean = true,
+    internal val extensionDefinitionPrefix: String? = null
 )

src/test/kotlin/com/charleskorn/kaml/YamlReadingTest.kt

@@ -1021,7 +1021,9 @@ object YamlReadingTest : Spek({
                 """.trimIndent()
 
                 context("parsing that input") {
-                    val result = Yaml(extensionDefinitionPrefix = ".").parse(SimpleStructure.serializer(), input)
+                    val configuration = YamlConfiguration(extensionDefinitionPrefix = ".")
+                    val yaml = Yaml(configuration = configuration)
+                    val result = yaml.parse(SimpleStructure.serializer(), input)
 
                     it("deserializes it to a Kotlin object, replacing the reference to the extension with the extension") {
                         assert(result).toBe(SimpleStructure("Jamie"))