Notations.

We will use BNF-like notation (the standard notation for grammar) with the following convention:

• Typewriter font for terminal symbols (like this). Sequences of terminal symbols are the only thing reads (by definition). We use range of characters to simplify when needed (like 0...9 for 0123456789).
• Italic for non-terminal symbols (like that). Non-terminal symbols are meta-variables describing a set of sequences of terminal symbols. All non-terminal symbols we use are defined in this section (a := denotes such a definition)
• Square brackets [...] denotes optional components, curly brackets {...} denotes the repetition zero, one or more times of a component, curly brackets with a plus {...} denotes repetition one or more times of a component and vertical bar denotes ... ... alternate choices. Parentheses are used for grouping.
• Warning: sometimes, the syntax uses terminal symbol, like square brackets, which we use also with a scpecial meaning to describe the grammar. It is not easy to distinguish for instance the typewriter square brackets ([]) and the normal version ([]). When needed, we will clarify this by a remark.