diff --git a/.vscode/launch.json b/.vscode/launch.json
index 56a9821..ab064d4 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -4,6 +4,14 @@
     // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
     "version": "0.2.0",
     "configurations": [
+        {
+            "type": "antlr-debug",
+            "request": "launch",
+            "name": "Debug Current Grammar",
+            "input": "tests/input.txt",
+            "grammar": "${file}",
+            "visualParseTree": true
+        },
         {
             "type": "node",
             "request": "launch",
diff --git a/src/ParserRuleContext.ts b/src/ParserRuleContext.ts
index 89e78ae..e21b73b 100644
--- a/src/ParserRuleContext.ts
+++ b/src/ParserRuleContext.ts
@@ -221,11 +221,15 @@ export class ParserRuleContext implements ParseTree {
     }
 
     public getSourceInterval(): Interval {
-        if (this.start === null || this.stop === null) {
+        if (this.start === null) {
             return Interval.INVALID_INTERVAL;
-        } else {
-            return new Interval(this.start.tokenIndex, this.stop.tokenIndex);
         }
+
+        if (this.stop === null || this.stop.tokenIndex < this.start.tokenIndex) {
+            return new Interval(this.start.tokenIndex, this.start.tokenIndex - 1);
+        }
+
+        return new Interval(this.start.tokenIndex, this.stop.tokenIndex);
     }
 
     public depth(): number {
diff --git a/src/atn/DecisionInfo.ts b/src/atn/DecisionInfo.ts
index 451b7a8..0c7e8b8 100644
--- a/src/atn/DecisionInfo.ts
+++ b/src/atn/DecisionInfo.ts
@@ -205,7 +205,7 @@ export class DecisionInfo {
         this.predicateEvals = [];
     }
 
-    public toString1(): string {
+    public toString(): string {
         return "{" +
             "decision=" + this.decision +
             ", contextSensitivities=" + this.contextSensitivities.length +
diff --git a/src/atn/Transition.ts b/src/atn/Transition.ts
index 83df3ff..b8e344a 100644
--- a/src/atn/Transition.ts
+++ b/src/atn/Transition.ts
@@ -57,6 +57,10 @@ export abstract class Transition {
         return null;
     }
 
+    public toString(): string {
+        return "";
+    }
+
     public abstract get transitionType(): number;
     public abstract matches(symbol: number, minVocabSymbol: number, maxVocabSymbol: number): boolean;
 }
diff --git a/src/misc/Interval.ts b/src/misc/Interval.ts
index f028c74..af3c89d 100644
--- a/src/misc/Interval.ts
+++ b/src/misc/Interval.ts
@@ -20,14 +20,8 @@ export class Interval {
     private cachedHashCode: number;
 
     public constructor(start: number, stop: number) {
-        if (start <= stop) {
-            this.start = start;
-            this.stop = stop;
-        } else {
-            this.start = stop;
-            this.stop = start;
-        }
-
+        this.start = start;
+        this.stop = stop;
         this.cachedHashCode = Math.imul(651 + start, 31) + stop;
     }
 
@@ -136,11 +130,7 @@ export class Interval {
     }
 
     public toString(): string {
-        if (this.start === this.stop) {
-            return this.start.toString();
-        } else {
-            return this.start.toString() + ".." + this.stop.toString();
-        }
+        return `${this.start}..${this.stop}`;
     }
 
     public get length(): number {
diff --git a/src/misc/IntervalSet.ts b/src/misc/IntervalSet.ts
index 8684422..384045b 100644
--- a/src/misc/IntervalSet.ts
+++ b/src/misc/IntervalSet.ts
@@ -28,9 +28,15 @@ export class IntervalSet {
 
     private cachedHashCode: number | undefined;
 
-    public constructor(set?: IntervalSet) {
+    public constructor(set?: IntervalSet | number[]) {
         if (set) {
-            this.addSet(set);
+            if (Array.isArray(set)) {
+                for (const el of set) {
+                    this.addOne(el);
+                }
+            } else {
+                this.addSet(set);
+            }
         }
     }
 
diff --git a/src/tree/pattern/ParseTreePatternMatcher.ts b/src/tree/pattern/ParseTreePatternMatcher.ts
index 653bfa0..716a06c 100644
--- a/src/tree/pattern/ParseTreePatternMatcher.ts
+++ b/src/tree/pattern/ParseTreePatternMatcher.ts
@@ -62,7 +62,7 @@ import { TokenTagToken } from "./TokenTagToken.js";
  *
  * See `TestParseTreeMatcher` for lots of examples.
  * {@link ParseTreePattern} has two static helper methods:
- * {@link ParseTreePattern#findAll} and {@link ParseTreePattern#match} that
+ * {@link ParseTreePattern.findAll} and {@link ParseTreePattern#match} that
  * are easy to use but not super efficient because they create new
  * {@link ParseTreePatternMatcher} objects each time and have to compile the
  * pattern in string form before using it.
@@ -84,7 +84,7 @@ import { TokenTagToken } from "./TokenTagToken.js";
  *
  * Delimiters are `<` and `>`, with `\` as the escape string
  * by default, but you can set them to whatever you want using
- * {@link #setDelimiters}. You must escape both start and stop strings
+ * {@link ParseTreePatternMatcher.setDelimiters}. You must escape both start and stop strings
  * `\<` and `\>`.
  */
 export class ParseTreePatternMatcher {
diff --git a/tests/BitSet.spec.ts b/tests/api/BitSet.spec.ts
similarity index 98%
rename from tests/BitSet.spec.ts
rename to tests/api/BitSet.spec.ts
index f630ec6..9cd4ddb 100644
--- a/tests/BitSet.spec.ts
+++ b/tests/api/BitSet.spec.ts
@@ -6,7 +6,7 @@
 
 import { describe, expect, it } from "vitest";
 
-import { BitSet } from "../src/misc/BitSet.js";
+import { BitSet } from "../../src/misc/BitSet.js";
 
 describe("BitSet", () => {
     it("Initialize  with all bits set to false", () => {
diff --git a/tests/CharStream.spec.ts b/tests/api/CharStream.spec.ts
similarity index 99%
rename from tests/CharStream.spec.ts
rename to tests/api/CharStream.spec.ts
index 1f597a9..fe0f0a2 100644
--- a/tests/CharStream.spec.ts
+++ b/tests/api/CharStream.spec.ts
@@ -6,7 +6,7 @@
 
 import { describe, expect, it } from "vitest";
 
-import { CharStreamImpl as CharStream, IntStream, Interval } from "../src/index.js";
+import { CharStreamImpl as CharStream, IntStream, Interval } from "../../src/index.js";
 
 const unicodeInput = "Hello 👋, World! 😁";
 
diff --git a/tests/HashSet.spec.ts b/tests/api/HashSet.spec.ts
similarity index 97%
rename from tests/HashSet.spec.ts
rename to tests/api/HashSet.spec.ts
index 499269a..ae2398f 100644
--- a/tests/HashSet.spec.ts
+++ b/tests/api/HashSet.spec.ts
@@ -6,8 +6,8 @@
 
 import { describe, it, expect, beforeEach } from "vitest";
 
-import { HashSet } from "../src/misc/HashSet.js";
-import type { IComparable } from "../src/utils/helpers.js";
+import { HashSet } from "../../src/misc/HashSet.js";
+import type { IComparable } from "../../src/utils/helpers.js";
 
 class Number implements IComparable {
     public constructor(public value: number) { }
diff --git a/tests/IntervalSet.spec.ts b/tests/api/IntervalSet.spec.ts
similarity index 99%
rename from tests/IntervalSet.spec.ts
rename to tests/api/IntervalSet.spec.ts
index 8b74112..53a5484 100644
--- a/tests/IntervalSet.spec.ts
+++ b/tests/api/IntervalSet.spec.ts
@@ -6,7 +6,7 @@
 
 import { describe, it, expect } from "vitest";
 
-import * as antlr4 from "../src/index.js";
+import * as antlr4 from "../../src/index.js";
 
 // eslint-disable-next-line @typescript-eslint/naming-convention
 const IntervalSet = antlr4.IntervalSet;
diff --git a/tests/api/XPath.spec.ts b/tests/api/XPath.spec.ts
new file mode 100644
index 0000000..1856693
--- /dev/null
+++ b/tests/api/XPath.spec.ts
@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) The ANTLR Project. All rights reserved.
+ * Use of this file is governed by the BSD 3-clause license that
+ * can be found in the LICENSE.txt file in the project root.
+ */
+
+import { beforeAll, describe, expect, it } from "vitest";
+
+import { CharStream, CommonTokenStream, ParserRuleContext, XPath, type ParseTree, type TerminalNode } from "antlr4ng";
+
+import { ExprLexer } from "../generated/ExprLexer.js";
+import { ExprParser } from "../generated/ExprParser.js";
+
+describe("XPath", () => {
+    const input = "def f(x,y) { x = 3+4; y; ; }\ndef g(x) { return 1+2*x; }\n";
+    let parser!: ExprParser;
+    let parseTree: ParseTree;
+
+    const xpath = [
+        "/prog/func", // all funcs under prog at root
+        "/prog/*", // all children of prog at root
+        "/*/func", // all func kids of any root node
+        "prog", // prog must be root node
+        "/prog", // prog must be root node
+        "/*", // any root
+        "*", // any root
+        "//ID", // any ID in tree
+        "//expr/primary/ID",// any ID child of a primary under any expr
+        "//body//ID", // any ID under a body
+        "//'return'", // any 'return' literal in tree, matched by literal name
+        "//RETURN", // any 'return' literal in tree, matched by symbolic name
+        "//primary/*", // all kids of any primary
+        "//func/*/stat",	// all stat nodes grand kids of any func node
+        "/prog/func/'def'",	// all def literal kids of func kid of prog
+        "//stat/';'", // all ';' under any stat node
+        "//expr/primary/!ID",	// anything but ID under primary under any expr node
+        "//expr/!primary",	// anything but primary under any expr node
+        "//!*", // nothing anywhere
+        "/!*", // nothing at root
+        "//expr//ID", // any ID under any expression (tests antlr/antlr4#370)
+    ];
+    const expected = [
+        "[func, func]",
+        "[func, func]",
+        "[func, func]",
+        "[prog]",
+        "[prog]",
+        "[prog]",
+        "[prog]",
+        "[f, x, y, x, y, g, x, x]",
+        "[y, x]",
+        "[x, y, x]",
+        "[return]",
+        "[return]",
+        "[3, 4, y, 1, 2, x]",
+        "[stat, stat, stat, stat]",
+        "[def, def]",
+        "[;, ;, ;, ;]",
+        "[3, 4, 1, 2]",
+        "[expr, expr, expr, expr, expr, expr]",
+        "[]",
+        "[]",
+        "[y, x]",
+    ];
+
+    beforeAll(() => {
+        const lexer = new ExprLexer(CharStream.fromString(input));
+        const tokens = new CommonTokenStream(lexer);
+        parser = new ExprParser(tokens);
+        parseTree = parser.prog();
+    });
+
+    it("Successful matches", () => {
+        for (let i = 0; i < xpath.length; i++) {
+            const found = XPath.findAll(parseTree, xpath[i], parser);
+
+            const ruleNames: string[] = [];
+            for (const t of found) {
+                if (t instanceof ParserRuleContext) {
+                    const r = t;
+                    ruleNames.push(parser.ruleNames[r.ruleIndex]);
+                } else {
+                    const token = t as TerminalNode;
+                    ruleNames.push(token.getText());
+                }
+            }
+
+            const result = `[${ruleNames.join(", ")}]`;
+
+            expect(result, "path " + xpath[i] + " failed").to.equal(expected[i]);
+        }
+
+    });
+});
diff --git a/tests/fixtures/grammars/Expr.g4 b/tests/fixtures/grammars/Expr.g4
new file mode 100644
index 0000000..67e8441
--- /dev/null
+++ b/tests/fixtures/grammars/Expr.g4
@@ -0,0 +1,75 @@
+// $antlr-format alignTrailingComments true, columnLimit 150, minEmptyLines 1, maxEmptyLinesToKeep 1, reflowComments false, useTab false
+// $antlr-format allowShortRulesOnASingleLine false, allowShortBlocksOnASingleLine true, alignSemicolons hanging, alignColons hanging
+
+grammar Expr;
+
+prog
+    : func+
+    ;
+
+func
+    : 'def' ID '(' arg (',' arg)* ')' body
+    ;
+
+body
+    : '{' stat+ '}'
+    ;
+
+arg
+    : ID
+    ;
+
+stat
+    : expr ';'          # printExpr
+    | ID '=' expr ';'   # assign
+    | 'return' expr ';' # ret
+    | ';'               # blank
+    ;
+
+expr
+    : expr ('*' | '/') expr # MulDiv
+    | expr ('+' | '-') expr # AddSub
+    | primary               # prim
+    ;
+
+primary
+    : INT          # int
+    | ID           # id
+    | '(' expr ')' # parens
+    ;
+
+MUL
+    : '*'
+    ;
+
+DIV
+    : '/'
+    ;
+
+ADD
+    : '+'
+    ;
+
+SUB
+    : '-'
+    ;
+
+RETURN
+    : 'return'
+    ;
+
+ID
+    : [a-zA-Z]+
+    ;
+
+INT
+    : [0-9]+
+    ;
+
+NEWLINE
+    : '\r'? '\n' -> skip
+    ;
+
+WS
+    : [ \t]+ -> skip
+    ;