diff --git a/theatre/shared/src/globals.ts b/theatre/shared/src/globals.ts
index cbeb706..365f9bd 100644
--- a/theatre/shared/src/globals.ts
+++ b/theatre/shared/src/globals.ts
@@ -1,4 +1,13 @@
 const globals = {
+  /**
+   * If the schema of the redux store changes in a backwards-incompatible way, then this version number should be incremented.
+   *
+   * While this looks like semver, it is not. There are no patch numbers, so any change in this number is a breaking change.
+   *
+   * However, as long as the schema of the redux store is backwards-compatible, then we don't have to change this number.
+   *
+   * Since the 0.4.0 release, this number has not had to change.
+   */
   currentProjectStateDefinitionVersion: '0.4.0',
 }
 
diff --git a/theatre/shared/src/instanceTypes.ts b/theatre/shared/src/instanceTypes.ts
index ad30c34..8861ec5 100644
--- a/theatre/shared/src/instanceTypes.ts
+++ b/theatre/shared/src/instanceTypes.ts
@@ -13,8 +13,6 @@ import type {$IntentionalAny} from './utils/types'
  * The functions in this module are supposed to be a replacement for that.
  */
 
-// --
-
 export const isProject = typeAsserter<Project>('Theatre_Project')
 
 export const isSheet = typeAsserter<Sheet>('Theatre_Sheet')
diff --git a/theatre/shared/src/utils/SimpleCache.ts b/theatre/shared/src/utils/SimpleCache.ts
index 29913b1..6a06633 100644
--- a/theatre/shared/src/utils/SimpleCache.ts
+++ b/theatre/shared/src/utils/SimpleCache.ts
@@ -1,9 +1,20 @@
 import type {$IntentionalAny} from './types'
 
+/**
+ * A basic cache
+ */
 export default class SimpleCache {
+  /**
+   * NOTE this could also be a Map.
+   */
   protected _values: Record<string, unknown> = {}
   constructor() {}
 
+  /**
+   * get the cache item at `key` or produce it using `producer` and cache _that_.
+   *
+   * Note that this won't work if you change the producer, like `get(key, producer1); get(key, producer2)`.
+   */
   get<T>(key: string, producer: () => T): T {
     if (this.has(key)) {
       return this._values[key] as $IntentionalAny
@@ -14,6 +25,9 @@ export default class SimpleCache {
     }
   }
 
+  /**
+   * Returns true if the cache has an item at `key`.
+   */
   has(key: string): boolean {
     return this._values.hasOwnProperty(key)
   }
diff --git a/theatre/shared/src/utils/WeakMapWithGetOrSet.ts b/theatre/shared/src/utils/WeakMapWithGetOrSet.ts
index 0e8d09f..3437499 100644
--- a/theatre/shared/src/utils/WeakMapWithGetOrSet.ts
+++ b/theatre/shared/src/utils/WeakMapWithGetOrSet.ts
@@ -1,9 +1,17 @@
 import type {$IntentionalAny} from './types'
 
+/**
+ * A wrapper around a WeakMap that adds a convenient `getOrSet` method.
+ */
 export default class WeakMapWithGetOrSet<
   K extends object = {},
   V = any,
 > extends WeakMap<K, V> {
+  /**
+   * get the cache item at `key` or produce it using `producer` and cache _that_.
+   *
+   * Note that this won't work if you change the producer, like `getOrSet(key, producer1); getOrSet(key, producer2)`.
+   */
   getOrSet<T extends V>(key: K, producer: () => T): T {
     if (this.has(key)) {
       return this.get(key) as $IntentionalAny
diff --git a/theatre/shared/src/utils/niceNumberUtils.ts b/theatre/shared/src/utils/niceNumberUtils.ts
index 89d00f8..c9e26bf 100644
--- a/theatre/shared/src/utils/niceNumberUtils.ts
+++ b/theatre/shared/src/utils/niceNumberUtils.ts
@@ -2,7 +2,7 @@ import padEnd from 'lodash-es/padEnd'
 import logger from '@theatre/shared/logger'
 
 /**
- * Returns the _aesthetically pleasing_ (aka "nicest") number `c`, such that `a <= c <= b`.
+ * Returns the _most aesthetically pleasing_ (aka "nicest") number `c`, such that `a <= c <= b`.
  * This is useful when a numeric value is being "nudged" by the user (e.g. dragged via mouse pointer),
  * and we want to avoid setting it to weird value like `101.1239293814314`, when we know that the user
  * probably just meant `100`.
diff --git a/theatre/shared/src/utils/pointerDeep.ts b/theatre/shared/src/utils/pointerDeep.ts
index 4369b9d..c862329 100644
--- a/theatre/shared/src/utils/pointerDeep.ts
+++ b/theatre/shared/src/utils/pointerDeep.ts
@@ -2,6 +2,9 @@ import type {Pointer} from '@theatre/dataverse'
 import type {PathToProp} from './addresses'
 import type {$IntentionalAny} from './types'
 
+/**
+ * Points deep into a pointer, using `toAppend` as the path. This is _NOT_ type-safe, so use with caution.
+ */
 export default function pointerDeep<T>(
   base: Pointer<T>,
   toAppend: PathToProp,
diff --git a/theatre/shared/src/utils/removePathFromObject.ts b/theatre/shared/src/utils/removePathFromObject.ts
index 31ff1cf..778deaa 100644
--- a/theatre/shared/src/utils/removePathFromObject.ts
+++ b/theatre/shared/src/utils/removePathFromObject.ts
@@ -1,6 +1,18 @@
 import type {PathToProp} from './addresses'
 import type {$FixMe, $IntentionalAny, SerializableMap} from './types'
 
+/**
+ * Mutates `base` to remove the path `path` from it. And if deleting a key makes
+ * its parent object empty of keys, that parent object will be deleted too, and so on.
+ *
+ * If `path` is `[]`, then `base` it'll remove all props from `base`.
+ *
+ * Example:
+ * ```ts
+ * removePathFromObject({a: {b: 1, c: 2}}, ['a', 'b']) // base is mutated to: {a: {c: 2}}
+ * removePathFromObject({a: {b: 1}}, ['a', 'b']) // base is mutated to: {}, because base.a is now empty.
+ * ```
+ */
 export default function removePathFromObject(
   base: SerializableMap,
   path: PathToProp,
@@ -8,36 +20,52 @@ export default function removePathFromObject(
   if (typeof base !== 'object' || base === null) return
 
   if (path.length === 0) {
-    const keys = Object.keys(base)
-    for (const key of keys) {
+    for (const key of Object.keys(base)) {
       delete base[key]
     }
     return
   }
 
+  // if path is ['a', 'b', 'c'], then this will be ['a', 'b']
   const keysUpToLastKey = path.slice(0, path.length - 1)
+
   let cur: $IntentionalAny = base
+
+  // we use this weakmap to be able to get the parent of a a child object
   const childToParentMapping = new WeakMap()
 
+  // The algorithm has two passes.
+
+  // On the first pass, we traverse the path and keep note of parent->child relationships.
+  // We also can bail out early  if we find that the path doesn't exist.
   for (const key of keysUpToLastKey) {
     const parent = cur
     const child = parent[key as $FixMe]
 
     if (typeof child !== 'object' || child === null) {
+      // the path either doesn't exist, or it doesn't point to an object, so we can just return
       return
     } else {
+      // the path _does_ exist so far. let's note the parent-child relationship.
       childToParentMapping.set(child, parent)
       cur = child
     }
   }
+  // if path is ['a', 'b', 'c'], then this will be ['c', 'b', 'a']
   const keysReversed = path.slice().reverse()
+
+  // on the second pass, we traverse the path in reverse, and delete the keys,
+  // and also delete the parent objects if they become empty.
   for (const key of keysReversed) {
     delete cur[key]
-    if (Object.keys(cur).length === 0) {
+
+    // if the current object is _not_ empty, then we can stop here.
+    if (Object.keys(cur).length > 0) {
+      return
+    } else {
+      // otherwise, we need to delete the parent object too.
       cur = childToParentMapping.get(cur)!
       continue
-    } else {
-      return
     }
   }
 }
diff --git a/theatre/shared/src/utils/resolvedPromise.ts b/theatre/shared/src/utils/resolvedPromise.ts
index 4ac641d..5ed3078 100644
--- a/theatre/shared/src/utils/resolvedPromise.ts
+++ b/theatre/shared/src/utils/resolvedPromise.ts
@@ -1,2 +1,5 @@
+/**
+ * A resolved promise
+ */
 const resolvedPromise = new Promise<void>((r) => r())
 export default resolvedPromise
diff --git a/theatre/shared/src/utils/sanitizers.ts b/theatre/shared/src/utils/sanitizers.ts
index d4d3399..066a45e 100644
--- a/theatre/shared/src/utils/sanitizers.ts
+++ b/theatre/shared/src/utils/sanitizers.ts
@@ -3,7 +3,7 @@ import {InvalidArgumentError} from '@theatre/shared/utils/errors'
 
 const _validateSym = (
   val: string,
-  thingy: string,
+  thingy: string, // there are two unsolved problems in computer science: cache invalidation and naming things.
   range: [min: number, max: number],
 ): void | string => {
   if (typeof val !== 'string') {
@@ -15,6 +15,12 @@ const _validateSym = (
   }
 }
 
+/**
+ * Validates a name, so that:
+ * - It's a string
+ * - It doesn't have leading or trailing spaces
+ * - It's between 3 and 32 characters long
+ */
 export const validateName = (
   name: string,
   thingy: string,
@@ -28,6 +34,12 @@ export const validateName = (
   }
 }
 
+/**
+ * Validates an instanceId, so that:
+ * - It's a string
+ * - It doesn't have leading or trailing spaces
+ * - It's between 1 and 32 characters long
+ */
 export const validateInstanceId = (
   name: string,
   thingy: string,
diff --git a/theatre/shared/src/utils/setDeepImmutable.ts b/theatre/shared/src/utils/setDeepImmutable.ts
index 2f4b440..1ef8ddf 100644
--- a/theatre/shared/src/utils/setDeepImmutable.ts
+++ b/theatre/shared/src/utils/setDeepImmutable.ts
@@ -1,10 +1,16 @@
+import type {PathToProp} from './addresses'
 import type {$IntentionalAny} from './types'
 import updateImmutable from './updateDeep'
 
+/**
+ * Returns an immutable clone of `obj`, with its `path` replaced with `replace`. This is _NOT_ type-safe, so use with caution.
+ *
+ * TODO Make a type-safe version of this, like ./mutableSetDeep.ts.
+ */
 export default function setDeepImmutable<S>(
-  state: S,
-  path: (string | number)[],
+  obj: S,
+  path: PathToProp,
   replace: $IntentionalAny,
 ): S {
-  return updateImmutable(state, path, () => replace) as $IntentionalAny as S
+  return updateImmutable(obj, path, () => replace) as $IntentionalAny as S
 }
diff --git a/theatre/shared/src/utils/slashedPaths.ts b/theatre/shared/src/utils/slashedPaths.ts
index 3c3c9de..9bfc54d 100644
--- a/theatre/shared/src/utils/slashedPaths.ts
+++ b/theatre/shared/src/utils/slashedPaths.ts
@@ -4,7 +4,9 @@ import {notify} from '@theatre/shared/notify'
 /**
  * Make the given string's "path" slashes normalized with preceding and trailing spaces.
  *
- * Prev "sanifySlashedPath".
+ * - It removes starting and trailing slashes: `/foo/bar/` becomes `foo / bar`
+ * - It adds wraps each slash with a single space, so that `foo/bar` becomes `foo / bar`
+ *
  */
 const normalizeSlashedPath = (p: string): string =>
   p
@@ -29,6 +31,11 @@ const getValidationErrorsOfSlashedPath = (p: string): void | string => {
   }
 }
 
+/**
+ * Sanitizes a `path` and warns the user if the input doesn't match the sanitized output.
+ *
+ * See {@link normalizeSlashedPath} for examples of how we do sanitization.
+ */
 export function validateAndSanitiseSlashedPathOrThrow(
   unsanitisedPath: string,
   fnName: string,
diff --git a/theatre/shared/src/utils/transformNumber.ts b/theatre/shared/src/utils/transformNumber.ts
index 4a68efd..4ddcc45 100644
--- a/theatre/shared/src/utils/transformNumber.ts
+++ b/theatre/shared/src/utils/transformNumber.ts
@@ -1,3 +1,6 @@
+/**
+ * Transforms `initialPos` by scaling and translating it around `origin`.
+ */
 export function transformNumber(
   initialPos: number,
   {
diff --git a/theatre/shared/src/utils/updateDeep.ts b/theatre/shared/src/utils/updateDeep.ts
index 62503ad..8491e19 100644
--- a/theatre/shared/src/utils/updateDeep.ts
+++ b/theatre/shared/src/utils/updateDeep.ts
@@ -1,13 +1,22 @@
 import type {$FixMe, $IntentionalAny} from './types'
 
-/* eslint-disable */
+/**
+ * Returns a new object with the value at `path` replaced with the result of `reducer(oldValue)`.
+ *
+ * Example:
+ * ```ts
+ * updateDeep({a: {b: 1}}, ['a', 'b'], (x) => x + 1) // {a: {b: 2}}
+ * updateDeep({a: {b: 1}}, [], (x) => Object.keys(x).length) // 1
+ * updateDeep({a: {b: 1}}, ['a', 'c'], (x) => (x ?? 0) + 1) // {a: {b: 1, c: 1}}
+ * ```
+ */
 export default function updateDeep<S>(
-  state: S,
+  obj: S,
   path: (string | number | undefined)[],
   reducer: (...args: $IntentionalAny[]) => $IntentionalAny,
 ): S {
-  if (path.length === 0) return reducer(state)
-  return hoop(state, path as $IntentionalAny, reducer)
+  if (path.length === 0) return reducer(obj)
+  return hoop(obj, path as $IntentionalAny, reducer)
 }
 
 const hoop = (
diff --git a/theatre/shared/src/utils/userReadableTypeOfValue.ts b/theatre/shared/src/utils/userReadableTypeOfValue.ts
index 5afacd5..260db3a 100644
--- a/theatre/shared/src/utils/userReadableTypeOfValue.ts
+++ b/theatre/shared/src/utils/userReadableTypeOfValue.ts
@@ -1,5 +1,20 @@
 import ellipsify from './ellipsify'
 
+/**
+ * Returns a short, user-readable description of the type of `value`.
+ * Examples:
+ * ```ts
+ * userReadableTypeOfValue(1) // 'number(1)'
+ * userReadableTypeOfValue(12345678901112) // 'number(1234567...)'
+ * userReadableTypeOfValue('hello') // 'string("hello")'
+ * userReadableTypeOfValue('hello world this is a long string') // 'string("hello wo...")'
+ * userReadableTypeOfValue({a: 1, b: 2}) // 'object'
+ * userReadableTypeOfValue([1, 2, 3]) // 'array'
+ * userReadableTypeOfValue(null) // 'null'
+ * userReadableTypeOfValue(undefined) // 'undefined'
+ * userReadableTypeOfValue(true) // 'true'
+ * ```
+ */
 const userReadableTypeOfValue = (v: unknown): string => {
   if (typeof v === 'string') {
     return `string("${ellipsify(v, 10)}")`