1# CSS [](https://pkg.go.dev/github.com/tdewolff/parse/v2/css?tab=doc)
2
3This package is a CSS3 lexer and parser written in [Go][1]. Both follow the specification at [CSS Syntax Module Level 3](http://www.w3.org/TR/css-syntax-3/). The lexer takes an io.Reader and converts it into tokens until the EOF. The parser returns a parse tree of the full io.Reader input stream, but the low-level `Next` function can be used for stream parsing to returns grammar units until the EOF.
4
5## Installation
6Run the following command
7
8 go get -u github.com/tdewolff/parse/v2/css
9
10or add the following import and run project with `go get`
11
12 import "github.com/tdewolff/parse/v2/css"
13
14## Lexer
15### Usage
16The following initializes a new Lexer with io.Reader `r`:
17``` go
18l := css.NewLexer(parse.NewInput(r))
19```
20
21To tokenize until EOF an error, use:
22``` go
23for {
24 tt, text := l.Next()
25 switch tt {
26 case css.ErrorToken:
27 // error or EOF set in l.Err()
28 return
29 // ...
30 }
31}
32```
33
34All tokens (see [CSS Syntax Module Level 3](http://www.w3.org/TR/css3-syntax/)):
35``` go
36ErrorToken // non-official token, returned when errors occur
37IdentToken
38FunctionToken // rgb( rgba( ...
39AtKeywordToken // @abc
40HashToken // #abc
41StringToken
42BadStringToken
43URLToken // url(
44BadURLToken
45DelimToken // any unmatched character
46NumberToken // 5
47PercentageToken // 5%
48DimensionToken // 5em
49UnicodeRangeToken
50IncludeMatchToken // ~=
51DashMatchToken // |=
52PrefixMatchToken // ^=
53SuffixMatchToken // $=
54SubstringMatchToken // *=
55ColumnToken // ||
56WhitespaceToken
57CDOToken // <!--
58CDCToken // -->
59ColonToken
60SemicolonToken
61CommaToken
62BracketToken // ( ) [ ] { }, all bracket tokens use this, Data() can distinguish between the brackets
63CommentToken // non-official token
64```
65
66### Examples
67``` go
68package main
69
70import (
71 "os"
72
73 "github.com/tdewolff/parse/v2/css"
74)
75
76// Tokenize CSS3 from stdin.
77func main() {
78 l := css.NewLexer(parse.NewInput(os.Stdin))
79 for {
80 tt, text := l.Next()
81 switch tt {
82 case css.ErrorToken:
83 if l.Err() != io.EOF {
84 fmt.Println("Error on line", l.Line(), ":", l.Err())
85 }
86 return
87 case css.IdentToken:
88 fmt.Println("Identifier", string(text))
89 case css.NumberToken:
90 fmt.Println("Number", string(text))
91 // ...
92 }
93 }
94}
95```
96
97## Parser
98### Usage
99The following creates a new Parser.
100``` go
101// true because this is the content of an inline style attribute
102p := css.NewParser(parse.NewInput(bytes.NewBufferString("color: red;")), true)
103```
104
105To iterate over the stylesheet, use:
106``` go
107for {
108 gt, _, data := p.Next()
109 if gt == css.ErrorGrammar {
110 break
111 }
112 // ...
113}
114```
115
116All grammar units returned by `Next`:
117``` go
118ErrorGrammar
119AtRuleGrammar
120EndAtRuleGrammar
121RulesetGrammar
122EndRulesetGrammar
123DeclarationGrammar
124TokenGrammar
125```
126
127### Examples
128``` go
129package main
130
131import (
132 "bytes"
133 "fmt"
134
135 "github.com/tdewolff/parse/v2/css"
136)
137
138func main() {
139 // true because this is the content of an inline style attribute
140 p := css.NewParser(parse.NewInput(bytes.NewBufferString("color: red;")), true)
141 out := ""
142 for {
143 gt, _, data := p.Next()
144 if gt == css.ErrorGrammar {
145 break
146 } else if gt == css.AtRuleGrammar || gt == css.BeginAtRuleGrammar || gt == css.BeginRulesetGrammar || gt == css.DeclarationGrammar {
147 out += string(data)
148 if gt == css.DeclarationGrammar {
149 out += ":"
150 }
151 for _, val := range p.Values() {
152 out += string(val.Data)
153 }
154 if gt == css.BeginAtRuleGrammar || gt == css.BeginRulesetGrammar {
155 out += "{"
156 } else if gt == css.AtRuleGrammar || gt == css.DeclarationGrammar {
157 out += ";"
158 }
159 } else {
160 out += string(data)
161 }
162 }
163 fmt.Println(out)
164}
165```
166
167## License
168Released under the [MIT license](https://github.com/tdewolff/parse/blob/master/LICENSE.md).
169
170[1]: http://golang.org/ "Go Language"