Traducción en curso
La cabecera de un documento HTML es la parte no mostrada en el navegador cuando se carga la página. La cual contiene información como
<title> de la página, enlaces a CSS (Si tú deseas estilizar tu contenido HTML con CSS), enlaces para personalizar favicons, y otros metadatos (datos sobre el HTML, como quien lo escribió, y palabras claves importantes que describen el documento). En este artículo abarcaremos todas las cosas antes mencionadas y más, para darte bases sólidas en el manejo del marcado y otros códigos que deberían estar presentes en tu cabecera.
|Prerequisitos:||Basic HTML familiarity, as covered in Getting started with HTML.|
aprender acerca de la cabeza HTML, cual es su proposito, los articuls mas importante que puede contener, y que efecto puede tener sobre el documento HTML.
¿Qué hay en la cabecera HTML?
Let's revisit the simple HTML document we covered in the previous article:
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>My test page</title> </head> <body> <p>This is my page</p> </body> </html>
La cabecera HTML está contenida por el elemento
<head> — a diferencia del contenido del elemento
<body> (el cual es mostrado en la página cargada por el navegador), el contenido de la cabecera no es mostrada en la pantalla de la página. En su lugar, el trabajo de la cabecera es contener metadatos acerca del documento. En el ejemplo anterior, la cabecera es bastante reducido.
<head> <meta charset="utf-8"> <title>My test page</title> </head>
En las páginas más grandes, sin embargo, la cabecera puede llegar a contener bastantes elementos - intente ir a algunos de sus sitios web favoritos y usando las herramientas de los desarrolladores [developer tools] compruebe el contenido de la cabecera. Nuestro objetivo aquí no es mostrarle cómo usar todo lo que puede ser empleado en la cabecera, sino enseñarle cómo usar los elemenos más obvias que deseará incluir en la cabecera y darle cierta familiaridad. Empecemos.
Añadiendo un título
Ya hemos visto el elemento
<title> en acción: se puede usar para agregar un título al documento. Sin embargo, esto puede confundirse con el elemento
<h1>, que se utiliza para agregar un encabezado en nivel superior del cuerpo de tu contenido, esto también se conoce como el título de la página. ¡Pero son cosas diferentes!
<h1>element appears on the page when loaded in the browser — generally this should be used once per page, to mark up the title of your page content (the story title, or news headline, or whatever is appropriate to your usage.)
<title>element is metadata that represents the title of the overall HTML document (not the document's content.)
Active learning: Inspecting a simple example
- To start off this active learning, we'd like you to go to our Github repo and download a copy of our title-example.html page. To do this, either
- Copy and paste the code out of the page and into a new text file in your code editor, then save it in a sensible place.
- Press the "Raw" button on the page, choose File > Save Page As... in your browser's menu, then choose a place to save the file.
- Now open the file in your browser. You should see something like this:
It should now be completely obvious where the
<h1>content appears, and where the
- You should also try opening the code up in your code editor, editing the contents of these elements, then refreshing the page in your browser. Have some fun with it.
<title> element contents are also used in other ways. For example, if you try bookmarking the page (Bookmarks > Bookmark This Page, in Firefox), you will see the
<title> contents filled in as the suggested bookmark name.
<title> contents are also used in search results, as you'll see below.
Metadata: the <meta> element
Metadata is data that describes data, and HTML has an "official" way of adding metadata to a document — the
<meta> element. Of course, the other stuff we are talking about in this article could also be thought of as metadata too. There are a lot of different types of
<meta> element that can be included in your page's <head>, but we won't try to explain them all at this stage, as it would just get too confusing. Instead, we'll explain a few things that you might commonly see, just to give you an idea.
Specifying your document's character encoding
In the example we saw above, this line was included:
This element simply specifies the document's character encoding — the character set that the document is permitted to use.
utf-8 is a universal character set that includes pretty much any character from any human language. This means that your web page will be able to handle displaying any language; it's therefore a good idea to set this on every web page you create! For example, your page could handle English and Japanese just fine:
If you set your character encoding to
ISO-8859-1, for example (the character set for the Latin alphabet), your page rendering would be all messed up:
Active learning: Experiment with character encoding
To try this out, revisit the simple HTML template you obtained in the previous section on
<title> (the title-example.html page), try changing the meta charset value to
ISO-8859-1, and add the Japanese to your page. This is the code we used:
<p>Japanese example: ご飯が熱い。</p>
Adding an author and description
<meta> elements include
namespecifies the type of meta element it is; what type of information it contains.
contentspecifies the actual meta content.
Two such meta elements that are useful to include on your page define the author of the page, and provide a concise description of the page. Let's look at an example:
<meta name="author" content="Chris Mills"> <meta name="description" content="The MDN Learning Area aims to provide complete beginners to the Web with all they need to know to get started with developing web sites and applications.">
Specifying an author is useful in a few ways: it is useful to be able to work out who wrote the page, if you want to contact them with questions about the content. Some content management systems have facilities to automatically extract page author information and make it available for such purposes.
Specifying a description that includes keywords relating to the content of your page is useful as it has the potential to make your page appear higher in relevant searches performed in search engines (such activities are termed Search Engine Optimization, or SEO.)
Active learning: The description's use in search engines
The description is also used on search engine result pages. Let's go through an exercise to explore this
- Go to the front page of The Mozilla Developer Network.
- View the page's source (Right/Ctrl + click on the page, choose View Page Source from the context menu.)
- Find the description meta tag. It will look like this:
<meta name="description" content="The Mozilla Developer Network (MDN) provides information about Open Web technologies including HTML, CSS, and APIs for both Web sites and HTML5 Apps. It also documents Mozilla products, like Firefox OS.">
- Now search for "Mozilla Developer Network" in your favourite search engine (We used Yahoo.) You'll notice the description
<title>element content used in the search result — definitely worth having!
Note: In Google, you will see some relevant subpages of MDN listed below the main MDN homepage link — these are called sitelinks, and are configurable in Google's webmaster tools — a way to make your site's search results better in the Google search engine.
<meta> features just aren't used any more. For example, the keyword
<meta> element — which is supposed to provide keywords for search engines to determine relevance of that page for different search terms — is ignored by search engines, because spammers were just filling the keyword list with hundreds of keywords, biasing results.
Other types of metadata
As you trawl around the Web, you'll find other types of metadata, too. A lot of the features you'll see on websites are proprietary creations, designed to provide certain sites (such as social networking sites) with specific pieces of information they can use.
For example, Open Graph Data is a metadata protocol that Facebook invented to provide richer metadata for websites. In the MDN sourcecode, you'll find this:
<meta property="og:image" content="https://developer.cdn.mozilla.net/static/img/opengraph-logo.dc4e08e2f6af.png"> <meta property="og:description" content="The Mozilla Developer Network (MDN) provides information about Open Web technologies including HTML, CSS, and APIs for both Web sites and HTML5 Apps. It also documents Mozilla products, like Firefox OS."> <meta property="og:title" content="Mozilla Developer Network">
One effect of this is that when you link to MDN on facebook, the link appears along with an image and description: a richer experience for users.
Twitter also has its own similar proprietary metadata, which has a similar effect when the site's URL is displayed on twitter.com. For example:
<meta name="twitter:title" content="Mozilla Developer Network">
Adding custom icons to your site
To further enrich your site design, you can add references to custom icons in your metadata, and these will be displayed in certain contexts.
The humble favicon, which has been around for many, many years, was the first icon of this type, a 16 x 16 pixel icon used in multiple places. The favicon can be added to your page by:
- Saving it in the same directory as the site's index page, saved in
.icoformat (most browsers will support favicons in more common formats like
.png, but using the ICO format will ensure it works as far back as Internet Explorer 6.)
- Adding the following line into your HTML
<head>to reference it:
<link rel="shortcut icon" href="favicon.ico" type="image/x-icon">
Modern browsers use favicons in various places, such as in the tab the page is open in, and in the bookmarks panel when you bookmark the page:
There are lots of other icon types to consider these days as well. For example, you'll find this in the source code of the MDN homepage:
<!-- third-generation iPad with high-resolution Retina display: --> <link rel="apple-touch-icon-precomposed" sizes="144x144" href="https://developer.cdn.mozilla.net/static/img/favicon144.a6e4162070f4.png"> <!-- iPhone with high-resolution Retina display: --> <link rel="apple-touch-icon-precomposed" sizes="114x114" href="https://developer.cdn.mozilla.net/static/img/favicon114.0e9fabd44f85.png"> <!-- first- and second-generation iPad: --> <link rel="apple-touch-icon-precomposed" sizes="72x72" href="https://developer.cdn.mozilla.net/static/img/favicon72.8ff9d87c82a0.png"> <!-- non-Retina iPhone, iPod Touch, and Android 2.1+ devices: --> <link rel="apple-touch-icon-precomposed" href="https://developer.cdn.mozilla.net/static/img/favicon57.a2490b9a2d76.png"> <!-- basic favicon --> <link rel="shortcut icon" href="https://developer.cdn.mozilla.net/static/img/favicon32.e02854fdcf73.png">
The comments explain what each icon is used for — these elements cover things like providing a nice high resolution icon to use when the website is saved to an iPad's home screen.
Don't worry too much about implementing all these types of icon right now — this is a fairly advanced feature, and you won't be expected to have knowledge of this to progress through the course. The main purpose here is to let you know what such things are, in case you come across them while browsing other web sites' source code.
<link> element and the
<script> element, respectively.
<link>element always goes inside the head of your document. This takes two attributes, rel="stylesheet", which indicates that it is the document's stylesheet, and href, which contains the path to the stylesheet file:
<link rel="stylesheet" href="my-css-file.css">
<script>element does not have to go in the head; in fact, often it is better to put it at the bottom of the document body (just before the closing
<script>element may look like an empty element, but it's not, and so needs a closing tag. Instead of pointing to an external script file, you can also choose to put your script inside the
- To start this active learning, grab a copy of our meta-example.html, script.js and style.css files, and save them on your local computer in the same directory. Make sure they are saved with the correct names and file extensions.
- Open the HTML file in both your browser, and your text editor.
- By following the information given above, add
If done correctly, when you save your HTML and refresh your browser you'll see that things have changed:
Note: If you get stuck in this exercise and can't get the CSS/JS to apply, try checking out our css-and-js.html example page.
Setting the primary language of the document
Finally, it's worth mentioning that you can (and really should) set the language of your page. This can be done by adding the lang attribute to the opening HTML tag (as seen in the meta-example.html and shown below.)
This is useful in many ways. Your HTML document will be indexed more effectively by search engines if its language is set (allowing it to appear correctly in language-specific results, for example), and it is useful to people with visual impairments using screen readers (for example, the word "six" exists in both French and English, but is pronounced differently.)
You can also set sub sections of your document to be recognised as different languages. For example, we could set our Japanese language section to be recognised as Japanese, like so:
<p>Japanese example: <span lang="jp">ご飯が熱い。</span>.</p>
That marks the end of our quickfire tour of the HTML head — there's a lot more you can do in here, but an exhaustive tour would be boring and confusing at this stage, and we just wanted to give you an idea of the most common things you'll find in there for now! In the next article we'll be looking at HTML text fundamentals.