diff --git a/package-lock.json b/package-lock.json
index 36c5019e1..ee52afbdb 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1624,6 +1624,12 @@
       "integrity": "sha512-mLQ4i2QO1ytvGWFWmcngKO//JXAQueZvwEKtjgQFM4jIK0kU+ytMfplL8j+n5mspOfjHwoAg+9yhb7BwAHm36g==",
       "dev": true
     },
+    "basic-auth": {
+      "version": "1.1.0",
+      "resolved": "https://registry.npmjs.org/basic-auth/-/basic-auth-1.1.0.tgz",
+      "integrity": "sha1-RSIe5Cn37h5QNb4/UVM/HN/SmIQ=",
+      "dev": true
+    },
     "bcrypt-pbkdf": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/bcrypt-pbkdf/-/bcrypt-pbkdf-1.0.2.tgz",
@@ -2300,6 +2306,12 @@
       "resolved": "https://registry.npmjs.org/core-util-is/-/core-util-is-1.0.2.tgz",
       "integrity": "sha1-tf1UIgqivFq1eqtxQMlAdUUDwac="
     },
+    "corser": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/corser/-/corser-2.0.1.tgz",
+      "integrity": "sha1-jtolLsqrWEDc2XXOuQ2TcMgZ/4c=",
+      "dev": true
+    },
     "crc-32": {
       "version": "1.2.0",
       "resolved": "https://registry.npmjs.org/crc-32/-/crc-32-1.2.0.tgz",
@@ -2742,6 +2754,18 @@
         "safer-buffer": "^2.1.0"
       }
     },
+    "ecstatic": {
+      "version": "3.3.2",
+      "resolved": "https://registry.npmjs.org/ecstatic/-/ecstatic-3.3.2.tgz",
+      "integrity": "sha512-fLf9l1hnwrHI2xn9mEDT7KIi22UDqA2jaCwyCbSUJh9a1V+LEUSL/JO/6TIz/QyuBURWUHrFL5Kg2TtO1bkkog==",
+      "dev": true,
+      "requires": {
+        "he": "^1.1.1",
+        "mime": "^1.6.0",
+        "minimist": "^1.1.0",
+        "url-join": "^2.0.5"
+      }
+    },
     "edge-paths": {
       "version": "2.2.1",
       "resolved": "https://registry.npmjs.org/edge-paths/-/edge-paths-2.2.1.tgz",
@@ -3240,6 +3264,12 @@
       "integrity": "sha512-i/2XbnSz/uxRCU6+NdVJgKWDTM427+MqYbkQzD321DuCQJUqOuJKIA0IM2+W2xtYHdKOmZ4dR6fExsd4SXL+WQ==",
       "dev": true
     },
+    "eventemitter3": {
+      "version": "4.0.7",
+      "resolved": "https://registry.npmjs.org/eventemitter3/-/eventemitter3-4.0.7.tgz",
+      "integrity": "sha512-8guHBZCwKnFhYdHr2ysuRWErTwhoN2X8XELRlrRwpmfeY2jjuUN4taQMsULKUVo1K4DvZl+0pgfyoysHxvmvEw==",
+      "dev": true
+    },
     "exit-on-epipe": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/exit-on-epipe/-/exit-on-epipe-1.0.1.tgz",
@@ -3566,6 +3596,12 @@
         "readable-stream": "^2.3.6"
       }
     },
+    "follow-redirects": {
+      "version": "1.14.1",
+      "resolved": "https://registry.npmjs.org/follow-redirects/-/follow-redirects-1.14.1.tgz",
+      "integrity": "sha512-HWqDgT7ZEkqRzBvc2s64vSZ/hfOceEol3ac/7tKwzuvEyWx3/4UegXh5oBOIotkGsObyk3xznnSRVADBgWSQVg==",
+      "dev": true
+    },
     "for-in": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/for-in/-/for-in-1.0.2.tgz",
@@ -4959,6 +4995,35 @@
       "integrity": "sha512-carPklcUh7ROWRK7Cv27RPtdhYhUsela/ue5/jKzjegVvXDqM2ILE9Q2BGn9JZJh1g87cp56su/FgQSzcWS8cQ==",
       "dev": true
     },
+    "http-proxy": {
+      "version": "1.18.1",
+      "resolved": "https://registry.npmjs.org/http-proxy/-/http-proxy-1.18.1.tgz",
+      "integrity": "sha512-7mz/721AbnJwIVbnaSv1Cz3Am0ZLT/UBwkC92VlxhXv/k/BBQfM2fXElQNC27BVGr0uwUpplYPQM9LnaBMR5NQ==",
+      "dev": true,
+      "requires": {
+        "eventemitter3": "^4.0.0",
+        "follow-redirects": "^1.0.0",
+        "requires-port": "^1.0.0"
+      }
+    },
+    "http-server": {
+      "version": "0.12.3",
+      "resolved": "https://registry.npmjs.org/http-server/-/http-server-0.12.3.tgz",
+      "integrity": "sha512-be0dKG6pni92bRjq0kvExtj/NrrAd28/8fCXkaI/4piTwQMSDSLMhWyW0NI1V+DBI3aa1HMlQu46/HjVLfmugA==",
+      "dev": true,
+      "requires": {
+        "basic-auth": "^1.0.3",
+        "colors": "^1.4.0",
+        "corser": "^2.0.1",
+        "ecstatic": "^3.3.2",
+        "http-proxy": "^1.18.0",
+        "minimist": "^1.2.5",
+        "opener": "^1.5.1",
+        "portfinder": "^1.0.25",
+        "secure-compare": "3.0.1",
+        "union": "~0.5.0"
+      }
+    },
     "http-signature": {
       "version": "1.2.0",
       "resolved": "https://registry.npmjs.org/http-signature/-/http-signature-1.2.0.tgz",
@@ -6201,6 +6266,12 @@
         "to-regex": "^3.0.2"
       }
     },
+    "mime": {
+      "version": "1.6.0",
+      "resolved": "https://registry.npmjs.org/mime/-/mime-1.6.0.tgz",
+      "integrity": "sha512-x0Vn8spI+wuJ1O6S7gnbaQg8Pxh4NNHb7KSINmEWKiPE4RKOplvijn+NkmYmmRgP68mc70j2EbeTFRsrswaQeg==",
+      "dev": true
+    },
     "mime-db": {
       "version": "1.47.0",
       "resolved": "https://registry.npmjs.org/mime-db/-/mime-db-1.47.0.tgz",
@@ -6848,6 +6919,12 @@
         "wrappy": "1"
       }
     },
+    "opener": {
+      "version": "1.5.2",
+      "resolved": "https://registry.npmjs.org/opener/-/opener-1.5.2.tgz",
+      "integrity": "sha512-ur5UIdyw5Y7yEj9wLzhqXiy6GZ3Mwx0yGI+5sMn2r0N0v3cKJvUmFH5yPP+WXh9e0xfyzyJX95D8l088DNFj7A==",
+      "dev": true
+    },
     "optionator": {
       "version": "0.8.2",
       "resolved": "https://registry.npmjs.org/optionator/-/optionator-0.8.2.tgz",
@@ -7120,6 +7197,46 @@
       "resolved": "https://registry.npmjs.org/pn/-/pn-1.1.0.tgz",
       "integrity": "sha512-2qHaIQr2VLRFoxe2nASzsV6ef4yOOH+Fi9FBOVH6cqeSgUnoyySPZkxzLuzd+RYOQTRpROA0ztTMqxROKSb/nA=="
     },
+    "portfinder": {
+      "version": "1.0.28",
+      "resolved": "https://registry.npmjs.org/portfinder/-/portfinder-1.0.28.tgz",
+      "integrity": "sha512-Se+2isanIcEqf2XMHjyUKskczxbPH7dQnlMjXX6+dybayyHvAf/TCgyMRlzf/B6QDhAEFOGes0pzRo3by4AbMA==",
+      "dev": true,
+      "requires": {
+        "async": "^2.6.2",
+        "debug": "^3.1.1",
+        "mkdirp": "^0.5.5"
+      },
+      "dependencies": {
+        "async": {
+          "version": "2.6.3",
+          "resolved": "https://registry.npmjs.org/async/-/async-2.6.3.tgz",
+          "integrity": "sha512-zflvls11DCy+dQWzTW2dzuilv8Z5X/pjfmZOWba6TNIVDm+2UDaJmXSOXlasHKfNBs8oo3M0aT50fDEWfKZjXg==",
+          "dev": true,
+          "requires": {
+            "lodash": "^4.17.14"
+          }
+        },
+        "debug": {
+          "version": "3.2.7",
+          "resolved": "https://registry.npmjs.org/debug/-/debug-3.2.7.tgz",
+          "integrity": "sha512-CFjzYYAi4ThfiQvizrFQevTTXHtnCqWfe7x1AhgEscTz6ZbLbfoLRLPugTQyBth6f8ZERVUSyWHFD/7Wu4t1XQ==",
+          "dev": true,
+          "requires": {
+            "ms": "^2.1.1"
+          }
+        },
+        "mkdirp": {
+          "version": "0.5.5",
+          "resolved": "https://registry.npmjs.org/mkdirp/-/mkdirp-0.5.5.tgz",
+          "integrity": "sha512-NKmAlESf6jMGym1++R0Ra7wvhV+wFW63FaSOFPwRahvea0gMUcGUhVeAg/0BC0wiv9ih5NYPB1Wn1UEI1/L+xQ==",
+          "dev": true,
+          "requires": {
+            "minimist": "^1.2.5"
+          }
+        }
+      }
+    },
     "posix-character-classes": {
       "version": "0.1.1",
       "resolved": "https://registry.npmjs.org/posix-character-classes/-/posix-character-classes-0.1.1.tgz",
@@ -7629,6 +7746,12 @@
       "integrity": "sha1-l/cXtp1IeE9fUmpsWqj/3aBVpNE=",
       "dev": true
     },
+    "requires-port": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/requires-port/-/requires-port-1.0.0.tgz",
+      "integrity": "sha1-kl0mAdOaxIXgkc8NpcbmlNw9yv8=",
+      "dev": true
+    },
     "requizzle": {
       "version": "0.2.3",
       "resolved": "https://registry.npmjs.org/requizzle/-/requizzle-0.2.3.tgz",
@@ -7759,6 +7882,12 @@
         "xmlchars": "^2.1.1"
       }
     },
+    "secure-compare": {
+      "version": "3.0.1",
+      "resolved": "https://registry.npmjs.org/secure-compare/-/secure-compare-3.0.1.tgz",
+      "integrity": "sha1-8aAymzCLIh+uN7mXTz1XjQypmeM=",
+      "dev": true
+    },
     "selenium-standalone": {
       "version": "7.1.0",
       "resolved": "https://registry.npmjs.org/selenium-standalone/-/selenium-standalone-7.1.0.tgz",
@@ -8979,6 +9108,15 @@
       "integrity": "sha1-XkvaMI5KiirlhPm5pDWaSZglzFA=",
       "dev": true
     },
+    "union": {
+      "version": "0.5.0",
+      "resolved": "https://registry.npmjs.org/union/-/union-0.5.0.tgz",
+      "integrity": "sha512-N6uOhuW6zO95P3Mel2I2zMsbsanvvtgn6jVqJv4vbVcz/JN0OkL9suomjQGmWtxJQXOCqUJvquc1sMeNz/IwlA==",
+      "dev": true,
+      "requires": {
+        "qs": "^6.4.0"
+      }
+    },
     "union-value": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/union-value/-/union-value-1.0.1.tgz",
@@ -9067,6 +9205,12 @@
       "integrity": "sha1-2pN/emLiH+wf0Y1Js1wpNQZ6bHI=",
       "dev": true
     },
+    "url-join": {
+      "version": "2.0.5",
+      "resolved": "https://registry.npmjs.org/url-join/-/url-join-2.0.5.tgz",
+      "integrity": "sha1-WvIvGMBSoACkjXuCxenC4v7tpyg=",
+      "dev": true
+    },
     "url-parse-lax": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/url-parse-lax/-/url-parse-lax-3.0.0.tgz",
diff --git a/package.json b/package.json
index 33ac92835..e83f97aa9 100644
--- a/package.json
+++ b/package.json
@@ -41,6 +41,7 @@
     "publish:beta": "gulp publishBeta",
     "recompile": "gulp recompile",
     "release": "gulp gitCreateRC",
+    "start": "http-server -o /tests/playground.html",
     "test": "tests/run_all_tests.sh",
     "test:generators": "tests/scripts/run_generators.sh",
     "test:compile:advanced": "gulp buildAdvancedCompilationTest",
@@ -78,6 +79,7 @@
     "gulp-shell": "^0.8.0",
     "gulp-sourcemaps": "^3.0.0",
     "gulp-umd": "^2.0.0",
+    "http-server": "^0.12.3",
     "js-green-licenses": "^3.0.0",
     "mocha": "^8.1.1",
     "readline-sync": "^1.4.10",
diff --git a/tests/playground.html b/tests/playground.html
index 3445811dd..11179a0db 100644
--- a/tests/playground.html
+++ b/tests/playground.html
@@ -151,10 +151,14 @@ function start() {
 }
 
 function setBackgroundColour() {
-  // Set background colour to differentiate server vs local copy.
-  if (location.protocol == 'file:') {
-    var lilac = '#d6d6ff';
-    document.body.style.backgroundColor = lilac;
+  // Set background colour to differentiate file: vs. localhost
+  // vs. server copy.
+  if (location.protocol === 'file:') {
+    document.body.style.backgroundColor = '#89A203';  // Unpleasant green.
+  } else if (location.hostname  === 'localhost' ||
+      location.hostname === '127.0.0.1' ||
+      location.hostname === '[::1]') {
+    document.body.style.backgroundColor = '#d6d6ff';  // Familliar lilac.
   }
 }
 
diff --git a/tests/playgrounds/advanced_playground.html b/tests/playgrounds/advanced_playground.html
index b142a6a00..6be7c1e42 100644
--- a/tests/playgrounds/advanced_playground.html
+++ b/tests/playgrounds/advanced_playground.html
@@ -172,10 +172,14 @@ function initPlayground() {
 }
 
 function setBackgroundColour() {
-  // Set background colour to differentiate server vs local copy.
+  // Set background colour to differentiate file: vs. localhost
+  // vs. server copy.
   if (location.protocol == 'file:') {
-    var lilac = '#d6d6ff';
-    document.body.style.backgroundColor = lilac;
+    document.body.style.backgroundColor = '#89A203';  // Unpleasant green.
+  } else if (location.hostname  === 'localhost' ||
+      location.hostname === '127.0.0.1' ||
+      location.hostname === '[::1]') {
+    document.body.style.backgroundColor = '#d6d6ff';  // Familliar lilac.
   }
 }