|   alternation
()  grouping
[]  option (0 or 1 times)
{}  repetition (0 to n times)
</pre>

<p>
Lower-case production names are used to identify lexical tokens.
Non-terminals are in CamelCase. Lexical tokens are enclosed in
double quotes <code>""</code> or back quotes <code>``</code>.
</p>

<p>
The form <code>a … b</code> represents the set of characters from
<code>a</code> through <code>b</code> as alternatives. The horizontal

// Single quotes and double quotes are recognized to prevent splitting within the
// quoted region, and are removed from the resulting substrings. If a quote in s
// isn't closed err will be set and r will have the unclosed argument as the
// last element. The backslash is used for escaping.
//
// For example, the following string:
//
//	`a b:"c d" 'e''f'  "g\""`
//
// Would be parsed as:
//

				in.invokeMacro(macro)
				continue
			}
			fallthrough
		default:
			if tok == scanner.EOF && len(in.ifdefStack) > 0 {
				// We're skipping text but have run out of input with no #endif.
				in.Error("unclosed #ifdef or #ifndef")
			}
			in.beginningOfLine = tok == '\n'
			if in.enabled() {
				in.text = in.Stack.Text()
				return tok
			}
		}
	}
	in.Error("recursive macro invocation")
	return 0

()  grouping
[]  option (0 or 1 times)
{}  repetition (0 to n times)
</pre>

<p>
Lowercase production names are used to identify lexical (terminal) tokens.
Non-terminals are in CamelCase. Lexical tokens are enclosed in
double quotes <code>""</code> or back quotes <code>``</code>.
</p>

<p>
The form <code>a … b</code> represents the set of characters from
<code>a</code> through <code>b</code> as alternatives. The horizontal

	{
		"3 #define foo bar\n",
		"'#' must be first item on line",
	},
	{
		"#ifdef foo\nhello",
		"unclosed #ifdef or #ifndef",
	},
	{
		"#ifndef foo\nhello",
		"unclosed #ifdef or #ifndef",
	},
	{
		"#ifdef foo\nhello\n#else\nbye",
		"unclosed #ifdef or #ifndef",
	},
	{
		"#define A() A()\nA()",
		"recursive macro invocation",
	},
	{