Editing Augmented Backus–Naur form (section)

===Core rules===

[[File:ABNF core rules.png|thumb|alt=ABNF syntax diagram of core rules|ABNF [[syntax diagram]] of core rules]]

The core rules are defined in the ABNF standard.
{|class="wikitable"
|- style="background-color: #efefef;"
!Rule!!Formal definition!!Meaning
|-
|ALPHA	|| {{codett|%x41–5A / %x61–7A		|abnf}} ||Upper- and lower-case ASCII letters (A–Z, a–z)
|-
|DIGIT 	|| {{codett|%x30–39			|abnf}} ||Decimal digits (0–9)
|-
|HEXDIG	|| {{codett|DIGIT / "A" / "B" / "C" / "D" / "E" / "F"	|abnf}} ||Hexadecimal digits (0–9, A–F, a–f)
|-
|DQUOTE 	|| {{codett|%x22				|abnf}} ||Double quote
|-
|SP		|| {{codett|%x20				|abnf}} ||Space
|-
|HTAB		|| {{codett|%x09				|abnf}} ||Horizontal tab
|-
|WSP		|| {{codett|SP / HTAB			|abnf}} ||Space and horizontal tab
|-
|LWSP		|| {{codett|*(WSP / CRLF WSP)	|abnf}} ||Linear white space (past newline)
|-
|VCHAR	|| {{codett|%x21–7E			|abnf}} ||Visible (printing) characters
|-
|CHAR	|| {{codett|%x01–7F			|abnf}} ||Any ASCII character, excluding NUL
|-
|OCTET	|| {{codett|%x00–FF			|abnf}} ||8 bits of data
|-
|CTL 		|| {{codett|%x00–1F / %x7F		|abnf}} ||Controls
|-
|CR		|| {{codett|%x0D				|abnf}} ||Carriage return
|-
|LF		|| {{codett|%x0A				|abnf}} ||Linefeed
|-
|CRLF		|| {{codett|CR LF			|abnf}} ||Internet-standard newline
|-
|BIT		|| {{codett|"0" / "1"			|abnf}} ||Binary digit
|-
|}

Note that in the core rules diagram the '''CHAR2''' charset is inlined in '''char-val''' and '''CHAR3''' is inlined in '''prose-val''' in the RFC spec. They are named here for clarity in the main syntax diagram.