diff --git a/developer/src/kmc-ldml/src/compiler/compiler.ts b/developer/src/kmc-ldml/src/compiler/compiler.ts
index f5f27c0a39..95b1aabee6 100644
--- a/developer/src/kmc-ldml/src/compiler/compiler.ts
+++ b/developer/src/kmc-ldml/src/compiler/compiler.ts
@@ -207,6 +207,13 @@ export class LdmlKeyboardCompiler {
       kmx.kmxplus[section.id] = sect as any;
     }
 
+    // give all sections a chance to postValidate
+    for(let section of sections) {
+      if(!section.postValidate(kmx.kmxplus[section.id])) {
+        passed = false;
+      }
+    }
+
     return passed ? kmx : null;
   }
 }
diff --git a/developer/src/kmc-ldml/src/compiler/section-compiler.ts b/developer/src/kmc-ldml/src/compiler/section-compiler.ts
index 8744059f7b..f200027786 100644
--- a/developer/src/kmc-ldml/src/compiler/section-compiler.ts
+++ b/developer/src/kmc-ldml/src/compiler/section-compiler.ts
@@ -1,8 +1,9 @@
 import { LDMLKeyboard, KMXPlus, CompilerCallbacks } from "@keymanapp/common-types";
 import { SectionIdent, constants } from '@keymanapp/ldml-keyboard-constants';
 
-/* istanbul ignore next */
-export class SectionCompiler {
+/** newable interface to SectionCompiler c'tor */
+export type SectionCompilerNew = new (source: LDMLKeyboard.LDMLKeyboardXMLSourceFile, callbacks: CompilerCallbacks) => SectionCompiler;
+export abstract class SectionCompiler {
   protected readonly keyboard3: LDMLKeyboard.LKKeyboard;
   protected readonly callbacks: CompilerCallbacks;
 
@@ -11,19 +12,34 @@ export class SectionCompiler {
     this.callbacks = callbacks;
   }
 
-  /* c8 ignore next 11 */
-  public get id(): SectionIdent {
-    throw Error(`Internal Error: id() not implemented`);
-  }
-
-  public compile(sections: KMXPlus.DependencySections): KMXPlus.Section {
-    throw Error(`Internal Error: compile() not implemented`);
-  }
+  public abstract get id(): SectionIdent;
 
+  /**
+   * This is called before compile.
+   * @returns false if this compiler failed to validate.
+   */
   public validate(): boolean {
     return true;
   }
 
+  /**
+   * Perform the compilation for this section, returning the correct Section subclass
+   * object.
+   *
+   * @param sections any declared dependency sections per dependencies()
+   */
+  public abstract compile(sections: KMXPlus.DependencySections): KMXPlus.Section;
+
+  /**
+   * This is called after all other compile phases have completed, and provides an
+   * opportunity for late error reporting, for example for invalid strings.
+   * @param section the compiled section, if any.
+   * @returns false if validate fails
+   */
+  public postValidate(section?: KMXPlus.Section): boolean {
+    return true;
+  }
+
   /**
    * Get the dependencies for this compiler.
    * @returns set of dependent sections
diff --git a/developer/src/kmc-ldml/src/compiler/tran.ts b/developer/src/kmc-ldml/src/compiler/tran.ts
index 89a9d61f1c..2e1944a7cc 100644
--- a/developer/src/kmc-ldml/src/compiler/tran.ts
+++ b/developer/src/kmc-ldml/src/compiler/tran.ts
@@ -19,7 +19,7 @@ import { MarkerTracker, MarkerUse } from "./marker-tracker.js";
 
 type TransformCompilerType = 'simple' | 'backspace';
 
-export class TransformCompiler<T extends TransformCompilerType, TranBase extends Tran> extends SectionCompiler {
+export abstract class TransformCompiler<T extends TransformCompilerType, TranBase extends Tran> extends SectionCompiler {
 
   static validateMarkers(keyboard: LDMLKeyboard.LKKeyboard, mt : MarkerTracker): boolean {
     keyboard?.transforms?.forEach(transforms =>
diff --git a/developer/src/kmc-ldml/test/helpers/index.ts b/developer/src/kmc-ldml/test/helpers/index.ts
index ea76da94b3..d21fe99498 100644
--- a/developer/src/kmc-ldml/test/helpers/index.ts
+++ b/developer/src/kmc-ldml/test/helpers/index.ts
@@ -4,7 +4,7 @@
 import 'mocha';
 import * as path from 'path';
 import { fileURLToPath } from 'url';
-import { SectionCompiler } from '../../src/compiler/section-compiler.js';
+import { SectionCompiler, SectionCompilerNew } from '../../src/compiler/section-compiler.js';
 import { KMXPlus, LDMLKeyboardXMLSourceFileReader, VisualKeyboard, CompilerEvent, LDMLKeyboardTestDataXMLSourceFile, compilerEventFormat, LDMLKeyboard, UnicodeSetParser, CompilerCallbacks } from '@keymanapp/common-types';
 import { LdmlKeyboardCompiler } from '../../src/main.js'; // make sure main.js compiles
 import { assert } from 'chai';
@@ -52,7 +52,7 @@ afterEach(function() {
 });
 
 
-export async function loadSectionFixture(compilerClass: typeof SectionCompiler, filename: string, callbacks: TestCompilerCallbacks, dependencies?: typeof SectionCompiler[]): Promise<Section> {
+export async function loadSectionFixture(compilerClass: SectionCompilerNew, filename: string, callbacks: TestCompilerCallbacks, dependencies?: SectionCompilerNew[], postValidateFail?: boolean): Promise<Section> {
   callbacks.messages = [];
   const inputFilename = makePathToFixture(filename);
   const data = callbacks.loadFile(inputFilename);
@@ -83,13 +83,16 @@ export async function loadSectionFixture(compilerClass: typeof SectionCompiler,
   compiler.dependencies.forEach(dep => assert.ok(sections[dep],
       `Required dependency '${dep}' for '${compiler.id}' was not supplied: Check the 'dependencies' argument to loadSectionFixture or testCompilationCases`));
 
-  return compiler.compile(sections);
+  const section = await compiler.compile(sections);
+  const postValidate = compiler.postValidate(section);
+  assert.equal(postValidate, !postValidateFail, `expected postValidate() to return ${!postValidateFail}`);
+  return section;
 }
 
 /**
  * Recursively load dependencies. Normally they are loaded in SECTION_COMPILERS order
  */
-async function loadDepsFor(sections: DependencySections, parentCompiler: SectionCompiler, source: LDMLKeyboardXMLSourceFile, callbacks: TestCompilerCallbacks, dependencies?: typeof SectionCompiler[]) {
+async function loadDepsFor(sections: DependencySections, parentCompiler: SectionCompiler, source: LDMLKeyboardXMLSourceFile, callbacks: TestCompilerCallbacks, dependencies?: SectionCompilerNew[]) {
   const parentId = parentCompiler.id;
   if (!dependencies) {
     // default dependencies
@@ -184,7 +187,11 @@ export interface CompilationCase {
   /**
    * Optional dependent sections to load.  Will be strs+list+elem if falsy.
    */
-  dependencies?: (typeof SectionCompiler)[];
+  dependencies?: (SectionCompilerNew)[];
+  /**
+   * Optional, if true, postValidate() must return false. (must be != postValidate())
+   */
+  postValidateFail?: boolean;
 }
 
 /**
@@ -193,7 +200,7 @@ export interface CompilationCase {
  * @param compiler argument to loadSectionFixture()
  * @param callbacks argument to loadSectionFixture()
  */
-export function testCompilationCases(compiler: typeof SectionCompiler, cases : CompilationCase[], dependencies?: (typeof SectionCompiler)[]) {
+export function testCompilationCases(compiler: SectionCompilerNew, cases : CompilationCase[], dependencies?: (SectionCompilerNew)[]) {
   // we need our own callbacks rather than using the global so messages don't get mixed
   const callbacks = new TestCompilerCallbacks();
   for (let testcase of cases) {