return "", err
			}
			return "", &Error{ErrInvalidNamedCapture, s}
		}

		capture := t[:end+1]        // "(?P<name>" or "(?<name>"
		name := t[exprStartPos:end] // "name"
		if err = checkUTF8(name); err != nil {
			return "", err
		}
		if !isValidCaptureName(name) {
			return "", &Error{ErrInvalidNamedCapture, capture}
		}

		// Like ordinary capture, but named.

		{"EmptyWordBoundary", Const, 0},
		{"ErrInternalError", Const, 0},
		{"ErrInvalidCharClass", Const, 0},
		{"ErrInvalidCharRange", Const, 0},
		{"ErrInvalidEscape", Const, 0},
		{"ErrInvalidNamedCapture", Const, 0},
		{"ErrInvalidPerlOp", Const, 0},
		{"ErrInvalidRepeatOp", Const, 0},
		{"ErrInvalidRepeatSize", Const, 0},
		{"ErrInvalidUTF8", Const, 0},
		{"ErrLarge", Const, 20},

pkg regexp/syntax, const ErrInvalidCharClass ErrorCode
pkg regexp/syntax, const ErrInvalidCharRange ErrorCode
pkg regexp/syntax, const ErrInvalidEscape ErrorCode
pkg regexp/syntax, const ErrInvalidNamedCapture ErrorCode
pkg regexp/syntax, const ErrInvalidPerlOp ErrorCode
pkg regexp/syntax, const ErrInvalidRepeatOp ErrorCode
pkg regexp/syntax, const ErrInvalidRepeatSize ErrorCode

pkg regexp/syntax, const ErrInvalidCharRange = "invalid character class range"
pkg regexp/syntax, const ErrInvalidEscape = "invalid escape sequence"
pkg regexp/syntax, const ErrInvalidNamedCapture = "invalid named capture"
pkg regexp/syntax, const ErrInvalidPerlOp = "invalid or unsupported Perl syntax"
pkg regexp/syntax, const ErrInvalidRepeatOp = "invalid nested repetition operator"