You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: scanner.go
    path of file: ./repos/corteza/server/vendor/github.com/gorilla/css/scanner
    
    the code of the file until where you have to start completion: // Copyright 2012 The Gorilla Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package scanner

import (
	"fmt"
	"regexp"
	"strings"
	"unicode"
	"unicode/utf8"
)

// tokenType identifies the type of lexical tokens.
type tokenType int

// String returns a string representation of the token type.
func (t tokenType) String() string {
	return tokenNames[t]
}

// Token represents a token and the corresponding string.
type Token struct {
	Type   tokenType
	Value  string
	Line   int
	Column int
}

// String returns a string representation of the token.
func (t *Token) String() string {
	if len(t.Value) > 10 {
		return fmt.Sprintf("%s (line: %d, column: %d): %.10q...",
			t.Type, t.Line, t.Column, t.Value)
	}
	return fmt.Sprintf("%s (line: %d, column: %d): %q",
		t.Type, t.Line, t.Column, t.Value)
}

// All tokens -----------------------------------------------------------------

// The complete list of tokens in CSS3.
const (
	// Scanner flags.
	TokenError tokenType = iota
	TokenEOF
	// From now on, only tokens from the CSS specification.
	TokenIdent
	TokenAtKeyword
	TokenString
	TokenHash
	TokenNumber
	TokenPercentage
	TokenDimension
	TokenURI
	TokenUnicodeRange
	TokenCDO
	TokenCDC
	TokenS
	TokenComment
	TokenFunction
	TokenIncludes
	TokenDashMatch
	TokenPrefixMatch
	TokenSuffixMatch
	TokenSubstringMatch
	TokenChar
	TokenBOM
)

// tokenNames maps tokenType's to their names. Used for conversion to string.
var tokenNames = map[tokenType]string{
	TokenError:          "error",
	TokenEOF:            "EOF",
	TokenIdent:          "IDENT",
	TokenAtKeyword:      "ATKEYWORD",
	TokenString:         "STRING",
	TokenHash:           "HASH",
	TokenNumber:         "NUMBER",
	TokenPercentage:     "PERCENTAGE",
	TokenDimension:      "DIMENSION",
	TokenURI:            "URI",
	TokenUnicodeRange:   "UNICODE-RANGE",
	TokenCDO:            "CDO",
	TokenCDC:            "CDC",
	TokenS:              "S",
	TokenComment:        "COMMENT",
	TokenFunction:       "FUNCTION",
	TokenIncludes:       "INCLUDES",
	TokenDashMatch:      "DASHMATCH",
	TokenPrefixMatch:    "PREFIXMATCH",
	TokenSuffixMatch:    "SUFFIXMATCH",
	TokenSubstringMatch: "SUBSTRINGMATCH",
	TokenChar:           "CHAR",
	TokenBOM:            "BOM",
}

// Macros and productions -----------------------------------------------------
// http://www.w3.org/TR/css3-syntax/#tokenization

var macroRegexp = regexp.MustCompile(`\{[a-z]+\}`)

// macros maps macro names to patterns to be expanded.
var macros = map[string]string{
    
func (s *Scanner) Next() *Token {
	if s.err != nil {
		return s.err
	}
	if s.pos >= len(s.input) {
		s.err = &Token{TokenEOF, "", s.row, s.col}
		return s.err
	}
	if s.pos == 0 {
		// Test BOM only once, at the beginning of the file.
		if strings.HasPrefix(s.input, "\uFEFF") {
			return s.emitSimple(TokenBOM, "\uFEFF")
		}
	}
	// There's a lot we can guess based on the first byte so we'll take a
	// shortcut before testing multiple regexps.
	input := s.input[s.pos:]
	switch input[0] {
	case '\t', '\n', '\f', '\r', ' ':
		// Whitespace.
		return s.emitToken(TokenS, matchers[TokenS].FindString(input))
	case '.':
		// Dot is too common to not have a quick check.
		// We'll test if this is a Char; if it is followed by a number it is a
		// dimension/percentage/number, and this will be matched later.
		if len(input) > 1 && !unicode.IsDigit(rune(input[1])) {
			return s.emitSimple(TokenChar, ".")
		}
	case '#':
		// Another common one: Hash or Char.
		if match := matchers[TokenHash].FindString(input); match != "" {
			return s.emitToken(TokenHash, match)
		}
		return s.emitSimple(TokenChar, "#")
	case '@':
		// Another common one: AtKeyword or Char.
		if match := matchers[TokenAtKeyword].FindString(input); match != "" {
			return s.emitSimple(TokenAtKeyword, match)
		}
		return s.emitSimple(TokenChar, "@")
	case ':', ',', ';', '%', '&', '+', '=', '>', '(', ')', '[', ']', '{', '}':
		// More common chars.
		return s.emitSimple(TokenChar, string(input[0]))
	case '"', '\'':
		// String or error.
		match := matchers[TokenString].FindString(input)
		if match != "" {
			return s.emitToken(TokenString, match)
		}

		s.err = &Token{TokenError, "unclosed quotation mark", s.row, s.col}
		return s.err
	case '/':
		// Comment, error or Char.
		if len(input) > 1 && input[1] == '*' {
			match := matchers[TokenComment].FindString(input)
			if match != "" {
				return s.emitToken(TokenComment, match)
			} else {
				s.err = &Token{TokenError, "unclosed comment", s.row, s.col}
				return s.err
			}
		}
		return s.emitSimple(TokenChar, "/")
	case '~':
		// Includes or Char.
		return s.emitPrefixOrChar(TokenIncludes, "~=")
	case '|':
		// DashMatch or Char.
		return s.emitPrefixOrChar(TokenDashMatch, "|=")
	case '^':
		// PrefixMatch or Char.
		return s.emitPrefixOrChar(TokenPrefixMatch, "^=")
	case '$':
		// SuffixMatch or Char.
		return s.emitPrefixOrChar(TokenSuffixMatch, "$=")
	case '*':
		// SubstringMatch or Char.
		return s.emitPrefixOrChar(TokenSubstringMatch, "*=")
	case '<':
		// CDO or Char.
		return s.emitPrefixOrChar(TokenCDO, "<!--")
	}
	// Test all regexps, in order.
	for _, token := range matchOrder {
		if match := matchers[token].FindString(input); match != "" {
			return s.emitToken(token, match)
		}
	}
	// We already handled unclosed quotation marks and comments,
	// so this can only be a Char.
	r, width := utf8.DecodeRuneInString(input)
	token := &Token{TokenChar, string(r), s.row, s.col}
	s.col += width
	s.pos += width
	return token
}