feat/fix: Large Book Update

pages/book/_meta.js

@@ -3,28 +3,43 @@ export default {
   guides: 'Guides',
   cs: 'Cheatsheets',
   cookbook: 'Cookbook',
-  '--': {
+  '-- 1': {
     type: 'separator',
+    title: 'Fundamentals of Tact',
   },
   types: 'Type system overview',
   integers: 'Integers',
-  functions: 'Functions',
+  operators: 'Operators',
   statements: 'Statements',
   constants: 'Constants',
+  functions: 'Functions',
   'composite-types': 'Composite types',
-  receive: 'Receive Messages',
-  bounced: 'Bounced Messages',
-  external: 'External Messages',
+  // <- a place for https://github.com/tact-lang/tact-docs/issues/115
+  '-- 2': {
+    type: 'separator',
+    title: 'Communication',
+  },
+  // <- NOTE
+  //    potential place for a rather short overview page describing asyncronous & actor-model nature
+  //    of TON Blockchain with respect to Tact and exchanging messages with it
+  receive: 'Receive messages',
+  bounced: 'Bounced messages',
+  external: 'External messages',
   lifecycle: 'Message lifecycle',
   send: 'Sending messages',
   'message-mode': 'Message mode',
-  deploy: 'Deploy contracts',
+  '-- 3': {
+    type: 'separator',
+    title: 'Going places',
+  },
+  deploy: 'Deployment',
   debug: 'Debugging',
   upgrades: 'Contract upgrades',
   import: 'Importing code',
-  masterchain: 'Masterchain',
-  func: 'Compatibility with Func',
   config: 'Configuration',
+  masterchain: 'Using masterchain',
+  func: 'Compatibility with FunC',
+  'exit-codes': 'Exit codes',
   programmatic: 'Programmatic API',
   '-- Community': {
     type: 'separator',

pages/book/composite-types.mdx

@@ -112,11 +112,11 @@ As it was mentioned in [type system overview](/book/types), most [primitive type
 
 [Variables](/book/statements#variable-declaration) or fields of [Structs](#structs) and [Messages](#messages) that can hold `null{:tact}` are called "optionals". They're useful to reduce state size when the variable isn't necesserily used.
 
-You can make any variable an optional by adding a question mark (`?`) after its type declaration. The only exceptions are [`map<>{:tact}`](/book/types#maps) and [`bounced<>{:tact}`](/book/bounced#bounced-messages-in-tact), where you can't make them, inner key/value type (in case of a map) or the inner [Message](#messages) (in case of a bounced) optional.
+You can make any variable of field an optional by adding a question mark (`?{:tact}`) after its type declaration. The only exceptions are [`map<>{:tact}`](/book/types#maps) and [`bounced<>{:tact}`](/book/bounced#bounced-messages-in-tact), where you can't make them, inner key/value type (in case of a map) or the inner [Message](#messages) (in case of a bounced) optional.
 
-Optional variables that are not defined hold the `null{:tact}` value by default. You cannot access them without checking for `null{:tact}` first. But if you're certain the optional variable is not `null{:tact}`, use the non-null assertion operator (`!!`, also called double-bang or double exclamation mark operator) to access its value.
+Optional variables or optional fields that are not defined hold the `null{:tact}` value by default. You cannot access them without checking for `null{:tact}` first. But if you're certain they are not `null{:tact}` at a given moment, use the non-null assertion operator (`!!{:tact}`) to access their value.
 
-Trying to access the value of an optional variable without using `!!` or checking for `null{:tact}` beforehand will result in a compilation error.
+Trying to access the value of an optional variable or an optional field without using `!!{:tact}` or without checking for `null{:tact}` beforehand will result in a compilation error.
 
 Example of optionals: