diff --git a/src/index.ts b/src/index.ts
index c9fe663..5f65eeb 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -8,11 +8,49 @@ export function char(c: string): CodePoint {
   return c.codePointAt(0) as CodePoint;
 }
 
+// Whitespace
+export const NEW_LINE: CodePoint = char('\n');
+export const CARRIAGE_RETURN: CodePoint = char('\r');
+export const SPACE: CodePoint = char(' ');
+export const TAB: CodePoint = char('\t');
+
+// Digit Boundaries
+export const DIGIT_0: CodePoint = char('0');
+export const DIGIT_9: CodePoint = char('9');
+
+export const DOT: CodePoint = char('.');
+
+// Hex Boundaries
+export const LOWERCASE_a: CodePoint = char('a');
+export const UPPERCASE_A: CodePoint = char('A');
+export const LOWERCASE_f: CodePoint = char('f');
+export const UPPERCASE_F: CodePoint = char('F');
+export const LOWERCASE_z: CodePoint = char('z');
+export const UPPERCASE_Z: CodePoint = char('Z');
+
+
+export function isBetween(a: CodePoint, x: CodePoint, b: CodePoint): boolean {
+  return a <= x && x <= b;
+}
+
+export function isDigit(x: CodePoint): boolean {
+  return isBetween(DIGIT_0, x, DIGIT_9);
+}
+
+export function isAlphanumeric(x: CodePoint): boolean {
+  return isDigit(x) || isBetween(LOWERCASE_a, x, LOWERCASE_z) || isBetween(LOWERCASE_z, x, UPPERCASE_Z);
+}
+
 export type CodePointRef = {
   char: CodePoint,
   offset: StringIndex, 
 };
 
+export type CodePointSpan = {
+  start: CodePointIndex,
+  end: CodePointIndex,
+}
+
 // === Source Text ===
 export class SourceText {
   readonly source: string;
@@ -147,6 +185,10 @@ export class SourceText {
     return { index, line, column };
   }
 
+  getSpan(span: CodePointSpan): Span {
+    return { start: this.getLocation(span.start), end: this.getLocation(span.end) };
+  }
+
   // Creates a SourceRegion from a Span.
   makeRegion(span: Span): SourceRegion {
     // Basic validation
@@ -202,6 +244,10 @@ export function span(start: SourceLocation, end: SourceLocation): Span {
   return { start, end };
 }
 
+export function rawSpan(start: CodePointIndex, end: CodePointIndex): CodePointSpan {
+  return { start, end };
+}
+
 export class SourceRegion {
   constructor(
     public readonly source: SourceText,
@@ -238,11 +284,11 @@ export class SourceRegion {
   }
 
   toString(): string {
-    return this.source.sliceByCp(this.span.start.index, this.span.end.index);
+    return this.stringOf(this.span);
   }
 
   stringOf(span: Span): string {
-    return this.subRegion(span).toString();
+    return this.source.sliceByCp(span.start.index, span.end.index);
   }
 
   // Returns a Span for the given line (1-based index).
@@ -292,24 +338,6 @@ export type SourceLocation = {
   column: number; // 1-based
 }
 
-// Whitespace
-export const NEW_LINE: CodePoint = char('\n');
-export const CARRIAGE_RETURN: CodePoint = char('\r');
-export const SPACE: CodePoint = char(' ');
-export const TAB: CodePoint = char('\t');
-
-// Digit Boundaries
-export const DIGIT_0: CodePoint = char('0');
-export const DIGIT_9: CodePoint = char('9');
-
-export const DOT: CodePoint = char('.');
-
-// Hex Boundaries
-export const LOWERCASE_a: CodePoint = char('a');
-export const UPPERCASE_A: CodePoint = char('A');
-export const LOWERCASE_f: CodePoint = char('f');
-export const UPPERCASE_F: CodePoint = char('F');
-
 // === Rendering Utilities ===
 
 export type LineView = {