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+# About the Language Reference
+
+Read the notation that the formal grammar uses.
+
+This part of the book describes the formal grammar of the Swift programming language.
+The grammar described here is intended to help you understand the language in more
+detail, rather than to allow you to directly implement a parser or compiler.
+
+The Swift language is relatively small, because many common types, functions, and operators
+that appear virtually everywhere in Swift code
+are actually defined in the Swift standard library. Although these types, functions,
+and operators aren't part of the Swift language itself,
+they're used extensively in the discussions and code examples in this part of the book.
+
+## How to Read the Grammar
+
+The notation used to describe the formal grammar of the Swift programming language
+follows a few conventions:
+
+- An arrow (→) is used to mark grammar productions and can be read as "can consist of."
+- Syntactic categories are indicated by *italic* text and appear on both sides
+  of a grammar production rule.
+- Literal words and punctuation are indicated by **`boldface constant width`** text
+  and appear only on the right-hand side of a grammar production rule.
+- Alternative grammar productions are separated by vertical
+  bars (|). When alternative productions are too long to read easily,
+  they're broken into multiple grammar production rules on new lines.
+- In a few cases, regular font text is used to describe the right-hand side
+  of a grammar production rule.
+- Optional syntactic categories and literals are marked by a trailing
+  question mark, *?*.
+
+As an example, the grammar of a getter-setter block is defined as follows:
+
+> Grammar of a getter-setter block:
+>
+> *getter-setter-block* → **`{`** *getter-clause* *setter-clause*_?_ **`}`** | **`{`** *setter-clause* *getter-clause* **`}`**
+
+This definition indicates that a getter-setter block can consist of a getter clause
+followed by an optional setter clause, enclosed in braces,
+*or* a setter clause followed by a getter clause, enclosed in braces.
+The grammar production above is equivalent to the following two productions,
+where the alternatives are spelled out explicitly:
+
+> Grammar of a getter-setter block:
+>
+>
+> *getter-setter-block* → **`{`** *getter-clause* *setter-clause*_?_ **`}`** \
+> *getter-setter-block* → **`{`** *setter-clause* *getter-clause* **`}`**
+
+<!--
+This source file is part of the Swift.org open source project
+
+Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+-->