Publishers of technology books, eBooks, and videos for creative people

Home > Articles

This chapter is from the book

This chapter is from the book

Combinators: Descendant and Child Selectors

So far, we've selected elements based on their individual qualities—their type and their class and id values. But we can also select elements based on their place in the document structure. We can select any element descended from another element, for example, any element of class chapter descended from a div element. Or we can get more specific, and specify that the element must be a child element (that is, contained directly within a particular element).

Descendant Selectors

The first of these two new kinds of selector is the descendant selector. It selects an element based on the elements that contain it (either directly, as their parent element, or as a container of their parent, and so on up the tree). We can select elements based on one containment relationship, or chain together selectors to make them more and more specific. Let's start with the simplest case, where we have just two elements.

In the last chapter, we cautioned against the indiscriminate addition of class and id values to elements, suggesting rather it makes sense to give an id value to significant, unique parts of a document (for example, the header part of a page, which will usually be a div element, which contains a heading and probably page or site navigation). Other common "landmarks" in a page include the main content of the page and footers. We'll look at page layout in great detail in Chapter 9, which will also focus on markup conventions for page layouts.

Let's suppose we have the main content block of our page contained within a div with class main (we've chosen this name from the ARIA landmarks, which we cover in detail in Chapter 6). Now, we can select only elements inside this element—for example, only paragraphs inside the main content—not those inside the footer or header using a descendent selector:

div#main p{
}

Rather than having to give a class of main to each paragraph in the main content div, we can use this descendant selector instead. Descendant selectors are the single most overlooked aspect of CSS in relation to their value. Learning to use id judiciously for marking up landmark elements and descendant selectors for selecting their contents is one of the most useful techniques you'll learn as a web developer.

Child Selectors

Child selectors are closely related to descendant selectors, but they differ both in their syntax, as well as what they select. They select descendant elements of other elements, but only when the element is a child of the first selected element—that is, only when it is directly contained within the first selected element. These can be useful in situations like those just discussed, but they give us even more specific ways to select elements based on the structure of the document.

Child selectors, instead of simply having a space between the component selectors, have a greater-than sign (>) between them. So, for example, to select only headings of level 2 that are directly inside the main div, we'd use this:

#main>h2{}

As mentioned, we can also chain together selectors to make them even more specific.

Chaining

Nested lists are a particularly good example of the ways in which chaining is useful. Lists can be nested several deep. Suppose we have a list such as this one:

<ul>
  <li>HTML and XHTML</li>

  <li><ul>
    <li>principles of markup</li>
    <li>syntax</li>
    <li>semantics</li>
    <li>validity</li>
    <li>accessibility</li>
  </ul></li>

  <li><ul>
    <li>HTML versions</li>
    <li><ul>
      <li>HTML 4.01</li>
      <li>XHTML 1.0, 1.1</li>
    </ul></li>
  </ul></li>
</ul>

Let's suppose we wanted to style only the list items nested three levels deep. We could do this by adding a class value to each such list item—though that's something we've suggested time and again that we should try to avoid. We should always see whether there's an approach using CSS before adding markup specifically for styling a document. The selector li will select every list item in the document, which won't do. Similarly, ul li will select all of the list items that are inside an unordered list. Now if we think about the structure, we know the elements we want to select are list items inside unordered lists, inside unordered lists, inside unordered lists. So, working backwards, our selector for these list items would be:

ul ul ul li {}

Similarly, we can select the second-level indented elements using this:

ul ul li {}

But, if you think it through a bit, we have a problem. A list that is nested three levels deep is also listed two levels deep. So this statement selects any lists that are nested either two or three levels deep. But let's suppose these lists are contained within the same div of id main. This selector will select the same lists (all of them being descendants of the main div):

#main ul ul li {}

On the other hand, if we want to select only those list items contained inside an ordered list that is itself contained inside an ordered list that is directly inside that the main div, we'd use:

div#main>ul ul li {}

This example shows how even seemingly intractable problems of selecting elements without resorting to adding class and id values solely for presentation can often, with some ingenuity, be solved with CSS selectors. In Chapter 12, we'll see how CSS3 provides microsurgical tools for selecting elements with CSS, but the most important thing is to start "thinking in CSS," which means really understanding and exploring selectors.

But, as you must be expecting by this point, there's just one little hitch. We've mentioned browser support for CSS in passing, and how it's long caused headaches for developers. In Chapter 7 we'll go into this whole issue in significant detail, but here's where we run into the issue in practical terms for the first time.

Although all modern browsers support child selectors, until Internet Explorer 7, Internet Explorer did not. This means that the reasonably large percentage of users who use IE 6 won't see any style applied using child selectors without the use of workarounds such as JavaScript libraries, which add support to IE for features it doesn't support. We'll go into this in detail in Chapter 7, so don't worry too much about the issue now.

Specificity of Child and Descendant Selectors

How does specificity work with selectors like these? Earlier we said that id selectors trump class selectors, which themselves trump type selectors. Often, that's all you need to know, but in the case of child and descendant selectors, which may be made up of type, class, and id selectors, how do we determine which is the more specific selector? Well, each different kind of selector is given a value. Type selectors are worth 1, class selectors are worth 10, and id selectors are worth 100. We then add up the total value of all the component selectors for a child or descendant selector. (Really.)

So this selector:

#main ul ul li
               

would be worth 103 (100 for the id selector, and 3 for the three type selectors), whereas this one:

chapter ul li
               

would be worth 12 (10 for the class selector, and 2 for the two type selectors). The selector with the highest value is the most specific, and it trumps any selectors with a lower specificity.

Note that this doesn't apply to group selectors. Instead of adding up the individual selectors in the group, we treat each of the comma-separated selectors in the group as belonging to different statements. So, for instance, this selector:

#main ul li, .chapter p
               

is really two selectors—one with a specificity of 102, and one of 12.

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Peachpit products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email ask@peachpit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.peachpit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020