diff --git a/src/index.ts b/src/index.ts
index d99eb10..21fc37e 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -74,11 +74,28 @@ export class SourceText {
     return this.source.slice(startOff, endOff);
   }
 
-  // Converts a linear Code Point Index into SourceLocation
-  // getLocation(index: CodePointIndex): SourceLocation {
-  //   // TODO: can be implemented either by a linear or binary search.
-  //   return (0 as any);
-  // }
+  // Converts a linear Code Point Index into a SourceLocation (line, column, index).
+  getLocation(index: CodePointIndex): SourceLocation {
+    // Does binary search.
+    let low = 0;
+    let high = this.lineStarts.length - 1;
+    let line = 1;
+    
+    while (low <= high) {
+      const mid = Math.floor((low + high) / 2);
+      if (this.lineStarts[mid] <= index) {
+        line = mid + 1;
+        low = mid + 1;
+      } else {
+        high = mid - 1;
+      }
+    }
+    
+    const lineStartIndex = this.lineStarts[line - 1];
+    const column = index - lineStartIndex + 1;
+    
+    return { index, line, column };
+  }
 
   // Returns the full text of a specific line (1-based index)
   getLineText(line: number): string {
@@ -114,6 +131,19 @@ export function sourceText(s: string): SourceText {
   return new SourceText(s);
 }
 
+export class SourceRegion {
+  // TODO
+  readonly sourceText: SourceText;
+  readonly span: Span;
+
+  constructor(sourceText: SourceText, span: Span) {
+    this.sourceText = sourceText;
+    // TODO: What about span validation?
+    this.span = span;
+  }
+}
+
+
 export type Span = {
   start: SourceLocation;
   end: SourceLocation;