diff --git a/package-lock.json b/package-lock.json
index be702943..38042b02 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -16,6 +16,7 @@
                 "@rollup/plugin-commonjs": "^25.0.7",
                 "@rollup/plugin-node-resolve": "^15.2.3",
                 "@rollup/plugin-terser": "^0.4.4",
+                "@types/sax": "^1.2.7",
                 "eslint": "^9.1.1",
                 "filesaver.js-npm": "latest",
                 "globals": "^15.0.0",
@@ -580,12 +581,30 @@
             "integrity": "sha512-/kYRxGDLWzHOB7q+wtSUQlFrtcdUccpfy+X+9iMBpHK8QLLhx2wIPYuS5DYtR9Wa/YlZAbIovy7qVdB1Aq6Lyw==",
             "dev": true
         },
+        "node_modules/@types/node": {
+            "version": "20.14.5",
+            "resolved": "https://registry.npmjs.org/@types/node/-/node-20.14.5.tgz",
+            "integrity": "sha512-aoRR+fJkZT2l0aGOJhuA8frnCSoNX6W7U2mpNq63+BxBIj5BQFt8rHy627kijCmm63ijdSdwvGgpUsU6MBsZZA==",
+            "dev": true,
+            "dependencies": {
+                "undici-types": "~5.26.4"
+            }
+        },
         "node_modules/@types/resolve": {
             "version": "1.20.2",
             "resolved": "https://registry.npmjs.org/@types/resolve/-/resolve-1.20.2.tgz",
             "integrity": "sha512-60BCwRFOZCQhDncwQdxxeOEEkbc5dIMccYLwbxsS4TUNeVECQ/pBJ0j09mrHOl/JJvpRPGwO9SvE4nR2Nb/a4Q==",
             "dev": true
         },
+        "node_modules/@types/sax": {
+            "version": "1.2.7",
+            "resolved": "https://registry.npmjs.org/@types/sax/-/sax-1.2.7.tgz",
+            "integrity": "sha512-rO73L89PJxeYM3s3pPPjiPgVVcymqU490g0YO5n5By0k2Erzj6tay/4lr1CHAAU4JyOWd1rpQ8bCf6cZfHU96A==",
+            "dev": true,
+            "dependencies": {
+                "@types/node": "*"
+            }
+        },
         "node_modules/abbrev": {
             "version": "1.0.9",
             "resolved": "https://registry.npmjs.org/abbrev/-/abbrev-1.0.9.tgz",
@@ -2865,6 +2884,12 @@
                 "node": "*"
             }
         },
+        "node_modules/undici-types": {
+            "version": "5.26.5",
+            "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-5.26.5.tgz",
+            "integrity": "sha512-JlCMO+ehdEIKqlFxk6IfVoAUVmgz7cU7zD/h9XZ0qzeosSHmUJVOzSQvvYSYWXkFXC+IfLKSIffhv0sVZup6pA==",
+            "dev": true
+        },
         "node_modules/universalify": {
             "version": "0.1.2",
             "resolved": "https://registry.npmjs.org/universalify/-/universalify-0.1.2.tgz",
diff --git a/package.json b/package.json
index 591b4d61..da0c1afc 100644
--- a/package.json
+++ b/package.json
@@ -44,6 +44,7 @@
         "@rollup/plugin-commonjs": "^25.0.7",
         "@rollup/plugin-node-resolve": "^15.2.3",
         "@rollup/plugin-terser": "^0.4.4",
+        "@types/sax": "^1.2.7",
         "eslint": "^9.1.1",
         "filesaver.js-npm": "latest",
         "globals": "^15.0.0",
diff --git a/src/main/js/doc.js b/src/main/js/doc.js
index e73b6bdb..f6420062 100644
--- a/src/main/js/doc.js
+++ b/src/main/js/doc.js
@@ -34,6 +34,14 @@ import { ComputedLength, hasOwnProperty, parseLength } from "./utils.js";
  * @module imscDoc
  */
 
+/**
+ * @typedef {import("./error").ErrorHandler} ErrorHandler
+ */
+
+/**
+ * @typedef {sax.Tag | sax.QualifiedTag} Node
+ */
+
 /**
  * Allows a client to provide callbacks to handle children of the <metadata> element
  * @typedef {Object} MetadataHandler
@@ -47,7 +55,7 @@ import { ComputedLength, hasOwnProperty, parseLength } from "./utils.js";
  * @callback OpenTagCallBack
  * @param {string} ns Namespace URI of the element
  * @param {string} name Local name of the element
- * @param {Object[]} attributes List of attributes, each consisting of a
+ * @param {Record<string, {uri: string, name: string, value: string}>} attributes List of attributes, each consisting of a
  *                              `uri`, `name` and `value`
  */
 
@@ -70,9 +78,9 @@ import { ComputedLength, hasOwnProperty, parseLength } from "./utils.js";
  * be called back when nodes are present in <metadata> elements.
  *
  * @param {string} xmlstring XML document
- * @param {?module:imscUtils.ErrorHandler} errorHandler Error callback
+ * @param {ErrorHandler} errorHandler Error callback
  * @param {?MetadataHandler} metadataHandler Callback for <Metadata> elements
- * @returns {Object} Opaque in-memory representation of an IMSC1 document
+ * @returns {?TT} Opaque in-memory representation of an IMSC1 document
  */
 
 export function fromXML(xmlstring, errorHandler, metadataHandler) {
@@ -807,19 +815,31 @@ function resolveTiming(doc, element, prev_sibling, parent) {
 
 }
 
-class ForeignElement {
+export class ForeignElement {
     constructor(node) {
         this.node = node;
     }
 }
 
-class TT {
+export class TT {
     constructor() {
+        /**
+         * @type {number[]}
+         */
         this.events = [];
         this.head = new Head();
+
+        /**
+         * @type {?Body}
+         */
         this.body = null;
     }
 
+    /**
+     * @param {Node} node
+     * @param {string} xmllang
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(node, xmllang, errorHandler) {
 
         /* compute cell resolution */
@@ -887,7 +907,9 @@ class TT {
         };
 
         /* xml:lang */
-
+        /**
+         * @type {string}
+         */
         this.lang = xmllang;
 
     }
@@ -922,10 +944,10 @@ class TT {
 
     }
 
-    /*
+    /**
      * Retrieves the range of ISD times covered by the document
      *
-     * @returns {Array} Array of two elements: min_begin_time and max_begin_time
+     * @returns {[number, number]} Array of two elements: min_begin_time and max_begin_time
      *
      */
     getMediaTimeRange() {
@@ -933,10 +955,10 @@ class TT {
         return [this.events[0], this.events[this.events.length - 1]];
     };
 
-    /*
+    /**
      * Returns list of ISD begin times
      *
-     * @returns {Array}
+     * @returns {number[]}
      */
     getMediaTimeEvents() {
 
@@ -948,7 +970,7 @@ class TT {
  * Represents a TTML Head element
  */
 
-class Head {
+export class Head {
     constructor() {
         this.styling = new Styling();
         this.layout = new Layout();
@@ -959,9 +981,16 @@ class Head {
  * Represents a TTML Styling element
  */
 
-class Styling {
+export class Styling {
     constructor() {
+        /**
+         * @type {Record<string, Style>}
+         */
         this.styles = {};
+
+        /**
+         * @type {Record<string, any>}
+         */
         this.initials = {};
     }
 }
@@ -970,13 +999,28 @@ class Styling {
  * Represents a TTML Style element
  */
 
-class Style {
+export class Style {
     constructor() {
+        /**
+         * @type {string}
+         */
         this.id = null;
+
+        /**
+         * @type {Record<string, any>}
+         */
         this.styleAttrs = null;
+
+        /**
+         * @type {string[]}
+         */
         this.styleRefs = null;
     }
 
+    /**
+     * @param {Node} node
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(node, errorHandler) {
         this.id = elementGetXMLID(node);
         this.styleAttrs = elementGetStyles(node, errorHandler);
@@ -988,11 +1032,17 @@ class Style {
  * Represents a TTML initial element
  */
 
-class Initial {
+export class Initial {
     constructor() {
+        /**
+         * @type {Record<string, string>}
+         */
         this.styleAttrs = null;
     }
 
+    /**
+     * @param {Node} node
+     */
     initFromNode(node) {
 
         this.styleAttrs = {};
@@ -1018,13 +1068,16 @@ class Initial {
  *
  */
 
-class Layout {
+export class Layout {
     constructor() {
         this.regions = {};
     }
 }
 
-class ContentElement {
+export class ContentElement {
+    /**
+     * @param {string} kind
+     */
     constructor(kind) {
         this.kind = kind;
     }
@@ -1034,13 +1087,32 @@ class ContentElement {
  * Represents a TTML image element
  */
 
-class Image extends ContentElement {
+export class Image extends ContentElement {
+    /**
+     * @param {string} src
+     * @param {string} type
+     */
     constructor(src, type) {
         super("image");
+
+        /**
+         * @type {string}
+         */
         this.src = src;
+
+        /**
+         * @type {string}
+         */
         this.type = type;
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     * @param {string} xmllang
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, parent, node, xmllang, errorHandler) {
         this.src = "src" in node.attributes ? node.attributes.src.value : null;
 
@@ -1068,31 +1140,56 @@ class Image extends ContentElement {
  *
  */
 
-class IdentifiedElement {
+export class IdentifiedElement {
+    /**
+     * @param {string} id
+     */
     constructor(id) {
         this.id = id;
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     */
     initFromNode(doc, parent, node) {
         this.id = elementGetXMLID(node);
     }
 }
 
-class LayoutElement {
+export class LayoutElement {
+    /**
+     * @param {string} id
+     */
     constructor(id) {
         this.regionID = id;
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     */
     initFromNode(doc, parent, node) {
         this.regionID = elementGetRegionID(node);
     }
 }
 
-class StyledElement {
+export class StyledElement {
+    /**
+     * @param {Record<string, any>} styleAttrs
+     */
     constructor(styleAttrs) {
         this.styleAttrs = styleAttrs;
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, parent, node, errorHandler) {
 
         this.styleAttrs = elementGetStyles(node, errorHandler);
@@ -1104,7 +1201,10 @@ class StyledElement {
     }
 }
 
-class AnimatedElement {
+export class AnimatedElement {
+    /**
+     * @param {any[]} sets
+     */
     constructor(sets) {
         this.sets = sets;
     }
@@ -1114,7 +1214,10 @@ class AnimatedElement {
     }
 }
 
-class ContainerElement {
+export class ContainerElement {
+    /**
+     * @param {string} contents
+     */
     constructor(contents) {
         this.contents = contents;
     }
@@ -1124,13 +1227,25 @@ class ContainerElement {
     }
 }
 
-class TimedElement {
+export class TimedElement {
+    /**
+     *
+     * @param {number} explicit_begin
+     * @param {number} explicit_end
+     * @param {number} explicit_dur
+     */
     constructor(explicit_begin, explicit_end, explicit_dur) {
         this.explicit_begin = explicit_begin;
         this.explicit_end = explicit_end;
         this.explicit_dur = explicit_dur;
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, parent, node, errorHandler) {
         const t = processTiming(doc, parent, node, errorHandler);
         this.explicit_begin = t.explicit_begin;
@@ -1145,11 +1260,17 @@ class TimedElement {
  * Represents a TTML body element
  */
 
-class Body extends ContentElement {
+export class Body extends ContentElement {
     constructor() {
         super("body");
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} node
+     * @param {string} xmllang
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, node, xmllang, errorHandler) {
         StyledElement.prototype.initFromNode.call(this, doc, null, node, errorHandler);
         TimedElement.prototype.initFromNode.call(this, doc, null, node, errorHandler);
@@ -1165,11 +1286,18 @@ class Body extends ContentElement {
  * Represents a TTML div element
  */
 
-class Div extends ContentElement {
+export class Div extends ContentElement {
     constructor() {
         super("div");
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     * @param {string} xmllang
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, parent, node, xmllang, errorHandler) {
         StyledElement.prototype.initFromNode.call(this, doc, parent, node, errorHandler);
         TimedElement.prototype.initFromNode.call(this, doc, parent, node, errorHandler);
@@ -1185,11 +1313,18 @@ class Div extends ContentElement {
  * Represents a TTML p element
  */
 
-class P extends ContentElement {
+export class P extends ContentElement {
     constructor() {
         super("p");
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     * @param {string} xmllang
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, parent, node, xmllang, errorHandler) {
         StyledElement.prototype.initFromNode.call(this, doc, parent, node, errorHandler);
         TimedElement.prototype.initFromNode.call(this, doc, parent, node, errorHandler);
@@ -1205,11 +1340,19 @@ class P extends ContentElement {
  * Represents a TTML span element
  */
 
-class Span extends ContentElement {
+export class Span extends ContentElement {
     constructor() {
         super("span");
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     * @param {string} xmllang
+     * @param {string} xmlspace
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, parent, node, xmllang, xmlspace, errorHandler) {
         StyledElement.prototype.initFromNode.call(this, doc, parent, node, errorHandler);
         TimedElement.prototype.initFromNode.call(this, doc, parent, node, errorHandler);
@@ -1226,11 +1369,19 @@ class Span extends ContentElement {
  * Represents a TTML anonymous span element
  */
 
-class AnonymousSpan extends ContentElement {
+export class AnonymousSpan extends ContentElement {
     constructor() {
         super("span");
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {string} text
+     * @param {string} xmlspace
+     * @param {string} xmllang
+     * @param {ErrorHandler} errorHandler
+     */
     initFromText(doc, parent, text, xmllang, xmlspace, errorHandler) {
         TimedElement.prototype.initFromNode.call(this, doc, parent, null, errorHandler);
 
@@ -1244,11 +1395,18 @@ class AnonymousSpan extends ContentElement {
  * Represents a TTML br element
  */
 
-class Br extends ContentElement {
+export class Br extends ContentElement {
     constructor() {
         super("br");
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     * @param {string} xmllang
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, parent, node, xmllang, errorHandler) {
         LayoutElement.prototype.initFromNode.call(this, doc, parent, node, errorHandler);
         TimedElement.prototype.initFromNode.call(this, doc, parent, node, errorHandler);
@@ -1262,9 +1420,13 @@ class Br extends ContentElement {
  *
  */
 
-class Region {
+export class Region {
     constructor() { }
 
+    /**
+     * @param {string} xmllang
+     * @returns {Region}
+     */
     createDefaultRegion(xmllang) {
         const r = new Region();
 
@@ -1280,6 +1442,12 @@ class Region {
         return r;
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} node
+     * @param {string} xmllang
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, node, xmllang, errorHandler) {
         IdentifiedElement.prototype.initFromNode.call(this, doc, null, node, errorHandler);
         TimedElement.prototype.initFromNode.call(this, doc, null, node, errorHandler);
@@ -1304,10 +1472,16 @@ class Region {
  *
  */
 
-class Set {
+export class Set {
     constructor() {
     }
 
+    /**
+     * @param {TT} doc
+     * @param {Node} parent
+     * @param {Node} node
+     * @param {ErrorHandler} errorHandler
+     */
     initFromNode(doc, parent, node, errorHandler) {
 
         TimedElement.prototype.initFromNode.call(this, doc, parent, node, errorHandler);
@@ -1341,14 +1515,27 @@ class Set {
  *
  */
 
+/**
+ * @param {Node} node
+ * @returns {string | null}
+ */
 function elementGetXMLID(node) {
     return node && "xml:id" in node.attributes ? node.attributes["xml:id"].value || null : null;
 }
 
+/**
+ * @param {Node} node
+ * @returns {string}
+ */
 function elementGetRegionID(node) {
     return node && "region" in node.attributes ? node.attributes.region.value : "";
 }
 
+/**
+ * @param {Node} node
+ * @param {ErrorHandler} errorHandler
+ * @returns {string}
+ */
 function elementGetTimeContainer(node, errorHandler) {
 
     const tc = node && "timeContainer" in node.attributes ? node.attributes.timeContainer.value : null;
@@ -1371,12 +1558,21 @@ function elementGetTimeContainer(node, errorHandler) {
 
 }
 
+/**
+ * @param {Node} node
+ * @returns {string[]}
+ */
 function elementGetStyleRefs(node) {
 
     return node && "style" in node.attributes ? node.attributes.style.value.split(" ") : [];
 
 }
 
+/**
+ * @param {Node} node
+ * @param {ErrorHandler} errorHandler
+ * @returns {Record<string, any>}
+ */
 function elementGetStyles(node, errorHandler) {
 
     const s = {};
@@ -1418,6 +1614,12 @@ function elementGetStyles(node, errorHandler) {
     return s;
 }
 
+/**
+ * @param {Node} node
+ * @param {string} ns
+ * @param {string} name
+ * @returns {string | null}
+ */
 function findAttribute(node, ns, name) {
     for (const i in node.attributes) {
 
@@ -1431,6 +1633,11 @@ function findAttribute(node, ns, name) {
     return null;
 }
 
+/**
+ * @param {Node} node
+ * @param {ErrorHandler} errorHandler
+ * @returns {number | null}
+ */
 function extractAspectRatio(node, errorHandler) {
 
     let ar = findAttribute(node, ns_ittp, "aspectRatio");
@@ -1475,9 +1682,12 @@ function extractAspectRatio(node, errorHandler) {
 
 }
 
-/*
+/**
  * Returns the cellResolution attribute from a node
  *
+ * @param {Node} node
+ * @param {ErrorHandler} errorHandler
+ * @returns {{w: number, h: number}}
  */
 function extractCellResolution(node, errorHandler) {
 
@@ -1512,6 +1722,11 @@ function extractCellResolution(node, errorHandler) {
 
 }
 
+/**
+ * @param {Node} node
+ * @param {ErrorHandler} errorHandler
+ * @returns {{ effectiveFrameRate: number, tickRate: number }}
+ */
 function extractFrameAndTickRate(node, errorHandler) {
 
     // subFrameRate is ignored per IMSC1 specification
@@ -1604,6 +1819,11 @@ function extractFrameAndTickRate(node, errorHandler) {
 
 }
 
+/**
+ * @param {Node} node
+ * @param {ErrorHandler} errorHandler
+ * @returns {{w: number, h: number} | null}
+ */
 function extractExtent(node, errorHandler) {
 
     const attr = findAttribute(node, ns_tts, "extent");
@@ -1635,6 +1855,12 @@ function extractExtent(node, errorHandler) {
 
 }
 
+/**
+ * @param {number} tickRate
+ * @param {number} effectiveFrameRate
+ * @param {string} str
+ * @returns {number | null}
+ */
 function parseTimeExpression(tickRate, effectiveFrameRate, str) {
 
     const CLOCK_TIME_FRACTION_RE = /^(\d{2,}):(\d\d):(\d\d(?:\.\d+)?)$/;
@@ -1700,6 +1926,13 @@ function parseTimeExpression(tickRate, effectiveFrameRate, str) {
     return r;
 }
 
+/**
+ * @param {TT} doc
+ * @param {Node} parent
+ * @param {Node} node
+ * @param {ErrorHandler} errorHandler
+ * @returns {{explicit_begin: number, explicit_end: number, explicit_dur: number}}
+ */
 function processTiming(doc, parent, node, errorHandler) {
 
     /* determine explicit begin */
@@ -1758,6 +1991,11 @@ function processTiming(doc, parent, node, errorHandler) {
 
 }
 
+/**
+ * @param {Styling} styling
+ * @param {Style} style
+ * @param {ErrorHandler} errorHandler
+ */
 function mergeChainedStyles(styling, style, errorHandler) {
 
     while (style.styleRefs.length > 0) {
@@ -1777,6 +2015,12 @@ function mergeChainedStyles(styling, style, errorHandler) {
 
 }
 
+/**
+ * @param {Styling} styling
+ * @param {string[]} stylerefs
+ * @param {Record<string, any>} styleattrs
+ * @param {ErrorHandler} errorHandler
+ */
 function mergeReferencedStyles(styling, stylerefs, styleattrs, errorHandler) {
 
     for (let i = stylerefs.length - 1; i >= 0; i--) {
@@ -1794,6 +2038,10 @@ function mergeReferencedStyles(styling, stylerefs, styleattrs, errorHandler) {
 
 }
 
+/**
+ * @param {Record<string, any>} from_styles
+ * @param {Record<string, any>} into_styles
+ */
 function mergeStylesIfNotPresent(from_styles, into_styles) {
 
     for (const sname in from_styles) {
@@ -1811,13 +2059,15 @@ function mergeStylesIfNotPresent(from_styles, into_styles) {
 
 /* TODO: validate style format at parsing */
 
-/*
+/**
  * Binary search utility function
  *
  * @typedef {Object} BinarySearchResult
  * @property {boolean} found Was an exact match found?
  * @property {number} index Position of the exact match or insert position
  *
+ * @param {number[]} arr
+ * @param {number} searchval
  * @returns {BinarySearchResult}
  */
 
diff --git a/src/main/js/error.js b/src/main/js/error.js
index 84c27f69..fc6b8e3d 100644
--- a/src/main/js/error.js
+++ b/src/main/js/error.js
@@ -3,6 +3,14 @@
  *
  */
 
+/**
+ * @module imscError
+ */
+
+/**
+ * @param {ErrorHandler} errorHandler
+ * @param {string} msg
+ */
 export function reportWarning(errorHandler, msg) {
 
   if (errorHandler && errorHandler.warn && errorHandler.warn(msg))
@@ -10,6 +18,10 @@ export function reportWarning(errorHandler, msg) {
 
 }
 
+/**
+ * @param {ErrorHandler} errorHandler
+ * @param {string} msg
+ */
 export function reportError(errorHandler, msg) {
 
   if (errorHandler && errorHandler.error && errorHandler.error(msg))
@@ -17,6 +29,10 @@ export function reportError(errorHandler, msg) {
 
 }
 
+/**
+ * @param {ErrorHandler} errorHandler
+ * @param {string} msg
+ */
 export function reportFatal(errorHandler, msg) {
 
   if (errorHandler && errorHandler.fatal)
@@ -25,3 +41,20 @@ export function reportFatal(errorHandler, msg) {
   throw msg;
 
 }
+
+/**
+ * Generic interface for handling events. The interface exposes four
+ * methods:
+ * - <pre>info</pre>: unusual event that does not result in an inconsistent state
+ * - <pre>warn</pre>: unexpected event that should not result in an inconsistent state
+ * - <pre>error</pre>: unexpected event that may result in an inconsistent state
+ * - <pre>fatal</pre>: unexpected event that results in an inconsistent state
+ *   and termination of processing
+ * Each method takes a single <pre>string</pre> describing the event as argument,
+ * and returns a single <pre>boolean</pre>, which terminates processing if <pre>true</pre>.
+ *
+ * @typedef {Object} ErrorHandler
+ * @property {(msg: string) => boolean} warn
+ * @property {(msg: string) => boolean} error
+ * @property {(msg: string) => boolean} fatal
+ */
diff --git a/src/main/js/html.js b/src/main/js/html.js
index bd0a557a..9a62ac70 100755
--- a/src/main/js/html.js
+++ b/src/main/js/html.js
@@ -27,6 +27,11 @@
 import { reportError } from "./error.js";
 import { byName } from "./styles.js";
 
+/**
+ * @typedef {import("./isd").ISD} ISD
+ * @typedef {import("./error").ErrorHandler} ErrorHandler
+ */
+
 /**
  * @module imscHTML
  */
@@ -36,7 +41,7 @@ const browserIsFirefox = /firefox/i.test(navigator.userAgent);
 /**
  * Function that maps <pre>smpte:background</pre> URIs to URLs resolving to image resource
  * @callback IMGResolver
- * @param {string} <pre>smpte:background</pre> URI
+ * @param {string} value <pre>smpte:background</pre> URI
  * @return {string} PNG resource URL
  */
 
@@ -56,8 +61,8 @@ const browserIsFirefox = /firefox/i.test(navigator.userAgent);
  * is called for the next ISD, otherwise <code>previousISDState</code> should be set to
  * <code>null</code>.
  *
- * @param {Object} isd ISD to be rendered
- * @param {Object} element Element into which the ISD is rendered
+ * @param {ISD} isd ISD to be rendered
+ * @param {HTMLElement} element Element into which the ISD is rendered
  * @param {?IMGResolver} imgResolver Resolve <pre>smpte:background</pre> URIs into URLs.
  * @param {?number} eheight Height (in pixel) of the child <div>div</div> or null
  *                  to use clientHeight of the parent element
@@ -65,10 +70,10 @@ const browserIsFirefox = /firefox/i.test(navigator.userAgent);
  *                  to use clientWidth of the parent element
  * @param {?boolean} displayForcedOnlyMode Value of the IMSC1 displayForcedOnlyMode parameter,
  *                   or false if null
- * @param {?module:imscUtils.ErrorHandler} errorHandler Error callback
- * @param {Object} previousISDState State saved during processing of the previous ISD, or null if initial call
+ * @param {?ErrorHandler} errorHandler Error callback
+ * @param {ISD} previousISDState State saved during processing of the previous ISD, or null if initial call
  * @param {?boolean} enableRollUp Enables roll-up animations (see CEA 708)
- * @return {Object} ISD state to be provided when this funtion is called for the next ISD
+ * @return {ISD} ISD state to be provided when this function is called for the next ISD
  */
 
 export function renderHTML(isd,
diff --git a/src/main/js/isd.js b/src/main/js/isd.js
index b3880e06..f3e677ad 100644
--- a/src/main/js/isd.js
+++ b/src/main/js/isd.js
@@ -32,15 +32,20 @@ import { ComputedLength, hasOwnProperty } from "./utils.js";
  * @module imscISD
  */
 
+/**
+ * @typedef {import("./doc").TT} TT
+ * @typedef {import("./error").ErrorHandler} ErrorHandler
+ */
+
 /**
  * Creates a canonical representation of an IMSC1 document returned by <pre>imscDoc.fromXML()</pre>
  * at a given absolute offset in seconds. This offset does not have to be one of the values returned
  * by <pre>getMediaTimeEvents()</pre>.
  *
- * @param {Object} tt IMSC1 document
+ * @param {TT} tt IMSC1 document
  * @param {number} offset Absolute offset (in seconds)
- * @param {?module:imscUtils.ErrorHandler} errorHandler Error callback
- * @returns {Object} Opaque in-memory representation of an ISD
+ * @param {ErrorHandler} errorHandler Error callback
+ * @returns {ISD} Opaque in-memory representation of an ISD
  */
 
 export function generateISD(tt, offset, errorHandler) {
@@ -720,15 +725,26 @@ function pruneEmptySpans(element) {
     }
 }
 
-class ISD {
+export class ISD {
     constructor(tt) {
+        /**
+         * @type {ISDContentElement[]}
+         */
         this.contents = [];
+
+        /**
+         * @type {string}
+         */
         this.aspectRatio = tt.aspectRatio;
+
+        /**
+         * @type {string}
+         */
         this.lang = tt.lang;
     }
 }
 
-class ISDContentElement {
+export class ISDContentElement {
     constructor(ttelem) {
 
         /* assume the element is a region if it does not have a kind */
diff --git a/src/main/js/styles.js b/src/main/js/styles.js
index df523e96..68423ed2 100644
--- a/src/main/js/styles.js
+++ b/src/main/js/styles.js
@@ -31,7 +31,22 @@ import { ComputedLength, parseColor, parseLength, parsePosition, parseTextShadow
  * @module imscStyles
  */
 
-class StylingAttributeDefinition {
+/**
+ * @typedef {import("./doc").TT} TT
+ * @typedef {import("./doc").Node} Node
+ */
+
+export class StylingAttributeDefinition {
+    /**
+     * @param {string} ns
+     * @param {string} name
+     * @param {string} initialValue
+     * @param {string[]} appliesTo
+     * @param {boolean} isInherit
+     * @param {boolean} isAnimatable
+     * @param {(value: string) => any} parseFunc
+     * @param {(doc: TT, parent: Node, element: Node, attr: string) => any} computeFunc
+     */
     constructor(ns, name, initialValue, appliesTo, isInherit, isAnimatable, parseFunc, computeFunc) {
         this.name = name;
         this.ns = ns;
@@ -1193,12 +1208,18 @@ export const all = [
 
 /* TODO: allow null parse function */
 
+/**
+ * @type {Record<string, StylingAttributeDefinition>}
+ */
 export const byQName = {};
 for (const i in all) {
 
     byQName[all[i].qname] = all[i];
 }
 
+/**
+ * @type {Record<string, StylingAttributeDefinition>}
+ */
 export const byName = {};
 for (const j in all) {
 
diff --git a/src/main/js/utils.js b/src/main/js/utils.js
index 5a682f5a..036d74e5 100644
--- a/src/main/js/utils.js
+++ b/src/main/js/utils.js
@@ -28,23 +28,6 @@
  * @module imscUtils
  */
 
-/* Documents the error handler interface */
-
-/**
- * @classdesc Generic interface for handling events. The interface exposes four
- * methods:
- * * <pre>info</pre>: unusual event that does not result in an inconsistent state
- * * <pre>warn</pre>: unexpected event that should not result in an inconsistent state
- * * <pre>error</pre>: unexpected event that may result in an inconsistent state
- * * <pre>fatal</pre>: unexpected event that results in an inconsistent state
- *   and termination of processing
- * Each method takes a single <pre>string</pre> describing the event as argument,
- * and returns a single <pre>boolean</pre>, which terminates processing if <pre>true</pre>.
- *
- * @name ErrorHandler
- * @class
- */
-
 /*
  * Parses a TTML color expression
  *
@@ -75,6 +58,10 @@ const NAMED_COLOR = {
     cyan: [0, 255, 255, 255],
 };
 
+/**
+ * @param {string} str
+ * @returns {[number, number, number, number]}
+ */
 export function parseColor(str) {
 
     let m;
@@ -115,6 +102,10 @@ export function parseColor(str) {
 
 const LENGTH_RE = /^((?:\+|-)?\d*(?:\.\d+)?)(px|em|c|%|rh|rw)$/;
 
+/**
+ * @param {string} str
+ * @returns {{ value: number, unit: string } | null}
+ */
 export function parseLength(str) {
 
     let m;
@@ -129,6 +120,10 @@ export function parseLength(str) {
     return r;
 };
 
+/**
+ * @param {string} str
+ * @returns {string | any[] | null}
+ */
 export function parseTextShadow(str) {
 
     const shadows = str.match(/([^(,)]|\([^)]+\))+/g);
@@ -202,6 +197,15 @@ export function parseTextShadow(str) {
     return r;
 };
 
+/**
+ * @typedef {{ value: number, unit: string }} Offset
+ * @typedef {{ edge: string, offset: Offset }} Position
+ */
+
+/**
+ * @param {string} str
+ * @returns {{h: Position, v: Position} | null}
+ */
 export function parsePosition(str) {
 
     /* see https://www.w3.org/TR/ttml2/#style-value-position */
@@ -327,15 +331,27 @@ export function parsePosition(str) {
 };
 
 export class ComputedLength {
+    /**
+     * @param {number} rw
+     * @param {number} rh
+     */
     constructor(rw, rh) {
         this.rw = rw;
         this.rh = rh;
     }
 
+    /**
+     * @param {number} width
+     * @param {number} height
+     * @returns {number}
+     */
     toUsedLength(width, height) {
         return width * this.rw + height * this.rh;
     };
 
+    /**
+     * @returns {boolean}
+     */
     isZero() {
         return this.rw === 0 && this.rh === 0;
     };
@@ -406,6 +422,11 @@ export function toComputedLength(lengthVal, lengthUnit, emLength, percentLength,
 
 }
 
+/**
+ * @param {Object} obj
+ * @param {string} prop
+ * @returns {boolean}
+ */
 export function hasOwnProperty(obj, prop) {
     return Object.prototype.hasOwnProperty.call(obj, prop);
 }