diff --git a/Jakefile.js b/Jakefile.js
index cf7f69d41dc..d46c2437ccb 100644
--- a/Jakefile.js
+++ b/Jakefile.js
@@ -131,7 +131,7 @@ var languageServiceLibrarySources = [
 
 var harnessCoreSources = [
     "harness.ts",
-    "vfs.ts",
+    "virtualFileSystem.ts",
     "sourceMapRecorder.ts",
     "harnessLanguageService.ts",
     "fourslash.ts",
@@ -163,7 +163,7 @@ var harnessSources = harnessCoreSources.concat([
     "cachingInServerLSHost.ts",
     "moduleResolution.ts",
     "tsconfigParsing.ts",
-    "expandFiles.ts"
+    "matchFiles.ts"
 ].map(function (f) {
     return path.join(unittestsDirectory, f);
 })).concat([
diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index a5cd7abc505..6935cf28bcd 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -582,9 +582,61 @@ namespace ts {
         return { options, errors };
     }
 
+    /**
+     * Tests for a path that ends in a recursive directory wildcard.
+     * Matches **, /**, /**\/, and /**\/, but not a**b.
+     *
+     * NOTE: used \/ in place of / above to avoid ending the comment.
+     *
+     * Breakdown:
+     *  (^|\/)      # matches either the beginning of the string or a directory separator.
+     *  \*\*        # matches the recursive directory wildcard "**".
+     *  \/?$        # matches an optional trailing directory separator at the end of the string.
+     */
     const invalidTrailingRecursionPattern = /(^|\/)\*\*\/?$/;
+
+    /**
+     * Tests for a path with multiple recursive directory wildcards.
+     * Matches **\/** and **\/a/**, but not **\/a**b.
+     *
+     * NOTE: used \/ in place of / above to avoid ending the comment.
+     *
+     * Breakdown:
+     *  (^|\/)      # matches either the beginning of the string or a directory separator.
+     *  \*\*\/      # matches a recursive directory wildcard "**" followed by a directory separator.
+     *  (.*\/)?     # optionally matches any number of characters followed by a directory separator.
+     *  \*\*        # matches a recursive directory wildcard "**"
+     *  ($|\/)      # matches either the end of the string or a directory separator.
+     */
     const invalidMultipleRecursionPatterns = /(^|\/)\*\*\/(.*\/)?\*\*($|\/)/;
 
+    /**
+     * Tests for a path containing a wildcard character in a directory component of the path.
+     * Matches /*\/, /?/, and /a*b/, but not /a/ or /a/*.
+     *
+     * NOTE: used \/ in place of / above to avoid ending the comment.
+     *
+     * Breakdown:
+     *  \/          # matches a directory separator.
+     *  [^/]*?      # matches any number of characters excluding directory separators (non-greedy).
+     *  [*?]        # matches either a wildcard character (* or ?)
+     *  [^/]*       # matches any number of characters excluding directory separators (greedy).
+     *  \/          # matches a directory separator.
+     */
+    const watchRecursivePattern = /\/[^/]*?[*?][^/]*\//;
+
+    /**
+     * Matches the portion of a wildcard path that does not contain wildcards.
+     * Matches /a of /a/*, or /a/b/c of /a/b/c/?/d.
+     *
+     * Breakdown:
+     *  ^                   # matches the beginning of the string
+     *  [^*?]*              # matches any number of non-wildcard characters
+     *  (?=\/[^/]*[*?])     # lookahead that matches a directory separator followed by
+     *                      # a path component that contains at least one wildcard character (* or ?).
+     */
+    const wildcardDirectoryPattern = /^[^*?]*(?=\/[^/]*[*?])/;
+
     /**
      * Expands an array of file specifications.
      *
@@ -693,9 +745,6 @@ namespace ts {
         return validSpecs;
     }
 
-    const watchRecursivePattern = /\/[^/]*?[*?][^/]*\//;
-    const wildcardDirectoryPattern = /^[^*?]*(?=\/[^/]*[*?])/;
-
     /**
      * Gets directories in a set of include patterns that should be watched for changes.
      */
diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index 509c193666f..f33cafc456d 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -23,7 +23,7 @@
 /// <reference path="external\chai.d.ts"/>
 /// <reference path="sourceMapRecorder.ts"/>
 /// <reference path="runnerbase.ts"/>
-/// <reference path="vfs.ts" />
+/// <reference path="virtualFileSystem.ts" />
 /* tslint:disable:no-null */
 
 // Block scoped definitions work poorly for global variables, temporarily enable var
diff --git a/src/harness/vfs.ts b/src/harness/virtualFileSystem.ts
similarity index 100%
rename from src/harness/vfs.ts
rename to src/harness/virtualFileSystem.ts
diff --git a/tests/cases/unittests/expandFiles.ts b/tests/cases/unittests/matchFiles.ts
similarity index 97%
rename from tests/cases/unittests/expandFiles.ts
rename to tests/cases/unittests/matchFiles.ts
index bbda14a2cfa..faccd31b88f 100644
--- a/tests/cases/unittests/expandFiles.ts
+++ b/tests/cases/unittests/matchFiles.ts
@@ -1,5 +1,6 @@
 /// <reference path="..\..\..\src\harness\external\mocha.d.ts" />
 /// <reference path="..\..\..\src\harness\harness.ts" />
+/// <reference path="..\..\..\src\harness\virtualFileSystem.ts" />
 
 namespace ts {
     class MockParseConfigHost extends Utils.VirtualFileSystem implements ParseConfigHost {
@@ -89,7 +90,7 @@ namespace ts {
         "c:/dev/f.other"
     ]);
 
-    describe("expandFiles", () => {
+    describe("matchFiles", () => {
         describe("with literal file list", () => {
             it("without exclusions", () => {
                 const json = {