Attribute selectors
===================

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As you know from your study of HTML, elements can have attributes that give further detail about the element being marked up. In CSS you can use attribute selectors to target elements with certain attributes. This lesson will show you how to use these very useful selectors.

|  |  |
| --- | --- |
| Prerequisites: | Basic software installed, basic knowledge of
 working with files, HTML basics (study
 Introduction to HTML), and an idea of how CSS works (study
 CSS first steps.)
  |
| Objective: | To learn what attribute selectors are and how to use them. |

Presence and value selectors
----------------------------

These selectors enable the selection of an element based on the presence of an attribute alone (for example `href`), or on various different matches against the value of the attribute.

| Selector | Example | Description |
| --- | --- | --- |
| `[*attr*]` | `a[title]` | 
 Matches elements with an *attr* attribute (whose name is the
 value in square brackets).
  |
| `[*attr*=*value*]` | `a[href="https://example.com"]` | 
 Matches elements with an *attr* attribute whose value is exactly
 *value* — the string inside the quotes.
  |
| `[*attr*~=*value*]` | `p[class~="special"]` | 
Matches elements with an *attr* attribute whose value is
 exactly *value*, or contains *value* in its (space
 separated) list of values.
  |
| `[*attr*|=*value*]` | `div[lang|="zh"]` | 
 Matches elements with an *attr* attribute whose value is exactly
 *value* or begins with *value* immediately followed by a
 hyphen.
  |

In the example below you can see these selectors being used.

* By using `li[class]` we can match any list item with a class attribute. This matches all of the list items except the first one.
* `li[class="a"]` matches a selector with a class of `a`, but not a selector with a class of `a` with another space-separated class as part of the value. It selects the second list item.
* `li[class~="a"]` will match a class of `a` but also a value that contains the class of `a` as part of a whitespace-separated list. It selects the second and third list items.

Substring matching selectors
----------------------------

These selectors allow for more advanced matching of substrings inside the value of your attribute. For example, if you had classes of `box-warning` and `box-error` and wanted to match everything that started with the string "box-", you could use `[class^="box-"]` to select them both (or `[class|="box"]` as described in section above).

| Selector | Example | Description |
| --- | --- | --- |
| `[attr^=value]` | `li[class^="box-"]` | Matches elements with an *attr* attribute, whose value begins with *value*. |
| `[attr$=value]` | `li[class$="-box"]` | Matches elements with an *attr* attribute whose value ends with *value*. |
| `[attr*=value]` | `li[class*="box"]` | Matches elements with an *attr* attribute whose value contains *value* anywhere within the string. |

(Aside: It may help to note that `^` and `$` have long been used as *anchors* in so-called *regular expressions* to mean *begins with* and *ends with* respectively.)

The next example shows usage of these selectors:

* `li[class^="a"]` matches any attribute value which starts with `a`, so matches the first two list items.
* `li[class$="a"]` matches any attribute value that ends with `a`, so matches the first and third list item.
* `li[class*="a"]` matches any attribute value where `a` appears anywhere in the string, so it matches all of our list items.

Case-sensitivity
----------------

If you want to match attribute values case-insensitively you can use the value `i` before the closing bracket. This flag tells the browser to match ASCII characters case-insensitively. Without the flag the values will be matched according to the case-sensitivity of the document language — in HTML's case it will be case sensitive.

In the example below, the first selector will match a value that begins with `a` — it only matches the first list item because the other two list items start with an uppercase A. The second selector uses the case-insensitive flag and so matches all of the list items.

**Note:** There is also a newer value `s`, which will force case-sensitive matching in contexts where matching is normally case-insensitive, however this is less well supported in browsers and isn't very useful in an HTML context.

Summary
-------

Now that we are done with attribute selectors, you can continue on to the next article and read about pseudo-class and pseudo-element selectors.

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