--- a/com/mojang/brigadier/tree/CommandNode.java
+++ b/com/mojang/brigadier/tree/CommandNode.java
@@ -3,6 +3,7 @@
 
 package com.mojang.brigadier.tree;
 
+// CHECKSTYLE:OFF
 import com.mojang.brigadier.AmbiguityConsumer;
 import com.mojang.brigadier.Command;
 import com.mojang.brigadier.RedirectModifier;
@@ -22,6 +23,7 @@
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 import java.util.function.Predicate;
+import net.minecraft.commands.CommandSourceStack;
 
 public abstract class CommandNode<S> implements Comparable<CommandNode<S>> {
     private final Map<String, CommandNode<S>> children = new LinkedHashMap<>();
@@ -32,6 +34,16 @@
     private final RedirectModifier<S> modifier;
     private final boolean forks;
     private Command<S> command;
+    public CommandNode<CommandSourceStack> clientNode; // Paper - Brigadier API
+    public CommandNode<io.papermc.paper.command.brigadier.CommandSourceStack> unwrappedCached = null; // Paper - Brigadier Command API
+    public CommandNode<io.papermc.paper.command.brigadier.CommandSourceStack> wrappedCached = null; // Paper - Brigadier Command API
+    // CraftBukkit start
+    public void removeCommand(String name) {
+        this.children.remove(name);
+        this.literals.remove(name);
+        this.arguments.remove(name);
+    }
+    // CraftBukkit end
 
     protected CommandNode(final Command<S> command, final Predicate<S> requirement, final CommandNode<S> redirect, final RedirectModifier<S> modifier, final boolean forks) {
         this.command = command;
@@ -61,7 +73,17 @@
         return this.modifier;
     }
 
-    public boolean canUse(final S source) {
+    // CraftBukkit start
+    public synchronized boolean canUse(final S source) {
+        if (source instanceof CommandSourceStack) {
+            try {
+                ((CommandSourceStack) source).currentCommand.put(Thread.currentThread(), this); // Paper - Thread Safe Vanilla Command permission checking
+                return this.requirement.test(source);
+            } finally {
+                ((CommandSourceStack) source).currentCommand.remove(Thread.currentThread()); // Paper - Thread Safe Vanilla Command permission checking
+            }
+        }
+        // CraftBukkit end
         return this.requirement.test(source);
     }
 
@@ -151,6 +173,12 @@
     protected abstract String getSortedKey();
 
     public Collection<? extends CommandNode<S>> getRelevantNodes(final StringReader input) {
+        // Paper start - prioritize mc commands in function parsing
+        return this.getRelevantNodes(input, null);
+    }
+    @org.jetbrains.annotations.ApiStatus.Internal
+    public Collection<? extends CommandNode<S>> getRelevantNodes(final StringReader input, final Object source) {
+        // Paper end - prioritize mc commands in function parsing
         if (this.literals.size() > 0) {
             final int cursor = input.getCursor();
             while (input.canRead() && input.peek() != ' ') {
@@ -158,7 +186,21 @@
             }
             final String text = input.getString().substring(cursor, input.getCursor());
             input.setCursor(cursor);
-            final LiteralCommandNode<S> literal = this.literals.get(text);
+            // Paper start - prioritize mc commands in function parsing
+            LiteralCommandNode<S> literal = null;
+            if (source instanceof CommandSourceStack css && css.source == net.minecraft.commands.CommandSource.NULL) {
+                if (!text.contains(":")) {
+                    literal = this.literals.get("minecraft:" + text);
+                }
+            } else if (source instanceof CommandSourceStack css && css.source instanceof net.minecraft.world.level.BaseCommandBlock) {
+                if (css.getServer().server.getCommandBlockOverride(text) && !text.contains(":")) {
+                    literal = this.literals.get("minecraft:" + text);
+                }
+            }
+            if (literal == null) {
+                literal = this.literals.get(text);
+            }
+            // Paper end - prioritize mc commands in function parsing
             if (literal != null) {
                 return Collections.singleton(literal);
             } else {
@@ -183,4 +225,11 @@
     }
 
     public abstract Collection<String> getExamples();
+    // Paper start - Brigadier Command API
+    public void clearAll() {
+        this.children.clear();
+        this.literals.clear();
+        this.arguments.clear();
+    }
+    // Paper end - Brigadier Command API
 }