WIP: WIP

WIP: not for review just yet. Doing tests in parallel to complete this
PR.

pages/book/debug.mdx

@@ -440,7 +440,7 @@ it('throws specific exit code', async () => {
 });
 ```
 
-Note, that to track down transactions with a certain exit code, you only need to specify `exitCode` field in `toHaveTransaction(){:typescript}` method of `expect(){:typescript}`.
+Note, that to track down transactions with a certain exit code, you only need to specify `exitCode` field in object argument to the `toHaveTransaction(){:typescript}` method of `expect(){:typescript}`.
 
 However, it's useful to narrow the scope by specifying the recipient address `to`, such that Jest would look only at the transaction caused by our message to the contract.
 

pages/book/operators.mdx

@@ -105,7 +105,7 @@ Unary operators can be one of the two types:
 
 ### Non-null assert, `!!` [#unary-non-null-assert]
 
-Unary double-exclamation mark (_non-null assertion_) operator `!!{:tact}` is a postfix operator, which enforces non-null values and allows direct access to the value of the optional variable if it's not `null{:tact}`. Raises a compilation error otherwise. Can be applied to any optional variable regardless of its non-null type.
+Unary double-exclamation mark (_non-null assertion_) operator `!!{:tact}` is a postfix operator, which enforces non-`null{:tact}` values and allows direct access to the value of the optional variable if it's not `null{:tact}`. Otherwise, raises a compilation error if the compiler can track it, and if not — throws an exception with [exit code 128](/book/exit-codes#128): `Null reference exception`. Can be applied to any optional variable regardless of its non-`null{:tact}` type.
 
 <Callout>
 

pages/book/optionals.mdx

@@ -10,7 +10,7 @@ You can make any variable or a field an optional by adding a question mark (`?{:
 
 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}`](/book/operators#unary-non-null-assert) to access their value.
 
-Trying to access the value of an optional variable or an optional field without using [`!!{:tact}`](/book/operators#unary-non-null-assert) or without 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}`](/book/operators#unary-non-null-assert) or without checking for `null{:tact}` beforehand will result in a compilation error if the compiler can track it, and if not — in an exception with [exit code 128](/book/exit-codes#128): `Null reference exception`.
 
 Example of optionals:
 

pages/book/structs-and-messages.mdx

@@ -100,9 +100,9 @@ message Add {
 }
 ```
 
-Messages are almost the same thing as [Structs](#structs) with the only difference that Messages have a 32-bit integer header in their serialization containing their unique numeric id. This allows Messages to be used with [receivers](/book/receive) since the contract can tell different types of messages apart based on this id.
+Messages are almost the same thing as [Structs](#structs) with the only difference that Messages have a 32-bit integer header in their serialization containing their unique numeric id, commonly referred to as an _opcode_ (operation code). This allows Messages to be used with [receivers](/book/receive) since the contract can tell different types of messages apart based on this id.
 
-Tact automatically generates those unique ids for every received Message, but this can be manually overwritten:
+Tact automatically generates those unique ids (opcodes) for every received Message, but this can be manually overwritten:
 
 ```tact
 // This Message overwrites its unique id with 0x7362d09c
@@ -111,7 +111,7 @@ message(0x7362d09c) TokenNotification {
 }
 ```
 
-This is useful for cases where you want to handle certain opcodes (operation codes) of a given smart contract, such as [Jetton standard](https://github.com/ton-blockchain/TEPs/blob/master/text/0074-jettons-standard.md). The short-list of opcodes this contract is able to process is [given here in FunC](https://github.com/ton-blockchain/token-contract/blob/main/ft/op-codes.fc). They serve as an interface to the smart contract.
+This is useful for cases where you want to handle certain opcodes of a given smart contract, such as [Jetton standard](https://github.com/ton-blockchain/TEPs/blob/master/text/0074-jettons-standard.md). The short-list of opcodes this contract is able to process is [given here in FunC](https://github.com/ton-blockchain/token-contract/blob/main/ft/op-codes.fc). They serve as an interface to the smart contract.
 
 <Callout>
 

pages/ref/core-advanced.mdx

@@ -196,7 +196,7 @@ fun nativeSendMessage(cell: Cell, mode: Int);
 fun nativeReserve(amount: Int, mode: Int);
 ```
 
-Calls native `raw_reserve` function with specified amount and mode. The `raw_reserve` is a function that creates an output action to reserve a specific amount of [nanoToncoins](book/integers#nanotoncoin) from the remaining balance of the account.
+Calls native `raw_reserve` function with specified amount and mode. The `raw_reserve` is a function that creates an output action to reserve a specific amount of [nanoToncoins](/book/integers#nanotoncoin) from the remaining balance of the account.
 
 It has the following signature in FunC:
 

pages/ref/core-debug.mdx

@@ -92,13 +92,20 @@ dump(null);
 dump(emit("msg".asComment())); // As emit() function doesn't return a value, dump() would print #DEBUG#: void.
 ```
 
+<Callout>
+
+  **Useful link:**\
+  [Debug with `dump(){:tact}`](/book/debug#tests-dump)
+
+</Callout>
+
 ## dumpStack
 
 ```tact
 fun dumpStack();
 ```
 
-Prints all the values of [persistent state variables](/book/contracts#variables) to the contract's debug console. Evaluated only if `debug` option is set in the [configuration file](/book/config), otherwise does nothing.
+Prints all the values of [persistent state variables](/book/contracts#variables) to the contract's debug console. Evaluated only if the `debug` option in the [configuration file](/book/config) is set to `true{:json}`, otherwise does nothing.
 
 Usage example:
 
@@ -113,6 +120,13 @@ contract DumpsterFire {
 }
 ```
 
+<Callout>
+
+  **Useful link:**\
+  [Debug with `dump(){:tact}`](/book/debug#tests-dump)
+
+</Callout>
+
 ## throw
 
 ```tact
@@ -129,6 +143,8 @@ fun nativeThrow(code: Int);
 
 Throws an exception with an error code equal to `code`. Execution of the current context stops (the statements after `nativeThrow` won't be executed) and control will be passed to the first [`try...catch{:tact}` block](/book/statements#try-catch) in the call stack. If no `try{:tact}` or `try...catch{:tact}` block exists among caller functions, [TVM](https://docs.ton.org/learn/tvm-instructions/tvm-overview) will terminate the transaction.
 
+Attempts to specify the `code` outside of $0 - 65535$ range cause an exception with [exit code 5](/book/exit-codes#5): `Integer out of expected range`.
+
 Usage examples:
 
 ```tact {2,7}
@@ -153,6 +169,8 @@ fun nativeThrowIf(code: Int, condition: Bool);
 
 Similar to [`nativeThrow(){:tact}`](#nativethrow), but throws an exception conditionally, when `condition` is equal to `true{:tact}`. Doesn't throw otherwise.
 
+Attempts to specify the `code` outside of $0 - 65535$ range cause an exception with [exit code 5](/book/exit-codes#5): `Integer out of expected range`.
+
 Usage examples:
 
 ```tact {2,7}
@@ -176,6 +194,8 @@ fun nativeThrowUnless(code: Int, condition: Bool);
 
 Similar to [`nativeThrow(){:tact}`](#nativethrow), but throws an exception conditionally, when `condition` is equal to `false{:tact}`. Doesn't throw otherwise.
 
+Attempts to specify the `code` outside of $0 - 65535$ range cause an exception with [exit code 5](/book/exit-codes#5): `Integer out of expected range`.
+
 Usage examples:
 
 ```tact {2,7}

pages/ref/core-strings.mdx

@@ -219,6 +219,8 @@ Returns a [`Slice{:tact}`][slice] out of the decoded [Base64](https://en.wikiped
 
 Note, that this function is limited and only takes the first $1023$ bits of data from the given [`String{:tact}`][p], without throwing an exception when the [`String{:tact}`][p] is larger (i.e. contains more than $1023$ bits of data).
 
+If the given [`String{:tact}`][p] contains characters not from the Base64 set, an exception with [exit code 134](/book/exit-codes#134) will be thrown: `Invalid argument`.
+
 Usage example:
 
 ```tact
@@ -263,6 +265,8 @@ Returns a new [`Slice{:tact}`][slice] out of the decoded [Base64](https://en.wik
 
 Note, that this function is limited and only takes the first $1023$ bits of data from the given [`Slice{:tact}`][slice], without throwing an exception if the [`Slice{:tact}`][slice] has more data (i.e., when it has any references).
 
+If the given [`Slice{:tact}`][slice] contains characters not from the Base64 set, an exception with [exit code 134](/book/exit-codes#134) will be thrown: `Invalid argument`.
+
 Usage example:
 
 ```tact
@@ -296,7 +300,7 @@ Extension function for the [`Int{:tact}`][int].
 
 Returns a [`String{:tact}`][p] from an [`Int{:tact}`][int] value using a [fixed-point representation](https://en.wikipedia.org/wiki/Fixed-point_arithmetic) of a fractional number, where `self` is a significant part of the number and `digits` is a number of digits in the fractional part.
 
-More precisely, `digits` is an exponentiation parameter of $10^{-\mathrm{digits}}$ expression, which gives the represented fractional number when multiplied by the actual [`Int{:tact}`][int] value. Parameter `digits` is required to be in the semi-closed interval: $0 <=$ `digits` $< 78$, otherwise an exception with [exit code 134](/book/exit-codes#134) will be thrown: `Invalid argument`.
+More precisely, `digits` is an exponentiation parameter of $10^{-\mathrm{digits}}$ expression, which gives the represented fractional number when multiplied by the actual [`Int{:tact}`][int] value. Parameter `digits` is required to be in the closed interval: $0 <$ `digits` $< 78$, otherwise an exception with [exit code 134](/book/exit-codes#134) will be thrown: `Invalid argument`.
 
 Usage example:
 

pages/ref/stdlib-dns.mdx

@@ -39,7 +39,7 @@ Source code (FunC): [dns.fc#L1](https://github.com/tact-lang/tact/blob/61541b778
 native dnsInternalNormalize(src: Slice): Slice;
 ```
 
-Normalizes the internal DNS representation of the [`Slice{:tact}`][slice].
+Normalizes the internal DNS representation of the [`Slice{:tact}`][slice]. The passed [`Slice{:tact}`][slice] must not have any references, otherwise an exception wit [exit code 134](/book/exit-codes#134) will be thrown: `Invalid argument`.
 
 Source code (FunC): [dns.fc#L125](https://github.com/tact-lang/tact/blob/61541b7783098e1af669faccd7d2334c10981c72/stdlib/libs/dns.fc#L125)