Macromedia Dreamweaver MX 2004 Demystified

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You'll probably spend more time using the various Dreamweaver Meta objects than using either of the other Head objects, but both link and base have their uses as well.

Base Tags and the Base Object

In HTML, the purpose of the base tag is to provide an absolute URL or a link target that the browser will automatically use to resolve all links within the document. It sounds more complicated than it is.

Base Tags and Absolute URLs

When a browser encounters relative URLs in an HTML document, it constructs absolute addresses from them by accessing a "base" URL, usually that of the current document itself. If your web page address is http://www.yourcompany.com/index.html and the page contains a link to images/spacer.gif , the browser combines those two addresses to construct an absolute URL for the image: http://www.yourcompany.com/images/spacer.gif .

If your document head uses the base tag to specify an alternate URL, like this:

<base href="http://www.webwidgets.com/store/">

all relative links in the document now are calculated relative to that address. So,

<a href="pricelist.html">Home</a>

resolves to this:

http://www.webwidgets.com/store/pricelist.html

Likewise,

<img src="../images/spacer.gif">

resolves to this:

http://www.webwidgets.com/images/spacer.gif

These addresses will be used even if the actual URL of your document is entirely different, like this:

http://www.homepagesRus.com/index.htm

When would you want to use the base tag to override your document's own URL for relative addressing? You would want to on two occasions:

Base Tags and Link Targets

Targets in links determine in which browser window a linked document will appear. Valid targets include the assigned name of any open window or frame in a frameset, or any of the generic targetssuch as _blank for a new window, or _top for the main window in a frameset. The normal link syntax looks like this:

<a href="widgets.html" target="_blank">

However, if the document head includes a base tag that points to a target, like this one, all links in the document are opened in that target window exactly as if the target were specified in each individual link:

<base target="_blank">

A link coded as this behaves as thought it were coded using the full targeting syntax:

<a href="widgets.html">

Why would you want to use the base tag to specify targets document-wide instead of specifying them individually for each link? It results in more efficient HTML, especially if your page contains many links (a resources or bibliography page, for instance). It makes life easier because you don't have to remember to specify every single target; it also makes editing simpler, if you change your mind about where links should be targeted . Instead of changing dozens of individual links, you need change only the base tag.

If you specify a target using the base tag, does that mean every single link in your document absolutely must use that target? Noyou can override the base target for specific links by specifying a different target for the link itself. So, if the <head> section specifies <base target="content">, but a link on the page specifies <a href="mypage.html" target="nav">, that particular link will open in the window named nav.

If you're a smart Dreamweaver user , of course, you could use a tag-specific Find and Replace to quickly change all those targets instead of using the base tag. Tag-specific searches are discussed in Chapter 27, "Writing Code in Dreamweaver."

Using the Base Tag in Dreamweaver

To insert a base tag into a Dreamweaver document, use the Base object in the Insert bar or menu, as shown in Figure 7.11. This object enables you to enter a URL and a target name. As with any head content, as long as you're in Design view when you insert it, it doesn't matter where the insertion point is when the object is chosen ; the base tag automatically is inserted into the head.

Figure 7.11. A base tag being inserted and later inspected, using the Base object.

Remember the following few tips when working with the base tag in the Dreamweaver environment:

Exercise 7.3. Add a Base Target to a Page's Links

Back to Walt's Web Widgets for this exercise. Walt has decided that he wants all the subject pages on his site to open in a new browser window so the visitor never leaves the home page. You can accomplish this quickly by adding a <base> tag specifying a target of _blank .

  1. From the chapter_07 folder, open main.html . Make sure that head content is showing, and that the Insert bar is showing the Head category. It doesn't matter what in the Document window you have selected.

  2. In the Insert bar, click the Base object. When the dialog box appears, leave the URL field empty. From the pop-up target menu, choose _blank . Click OK to exit the dialog box.

  3. Set the Document window to show Code and Design view. In the Head content display bar, click the Base object icon to select your newly inserted base tag. This action also should select the code for the base tag, in Code view.

  4. In Code view, delete the href attribute from the base tag so the tag reads as follows :

    <base target="_blank">

That's it! Preview the page in a browser and click any of the page's links. Each should open in a new window.

Link Tags and the Link Object

With the link tag, it's theoretically possible to specify all sorts of complex relationships between web documents. This includes specifying certain documents as next and previous in a series, linking alternative-language versions of pages, linking page glossaries, and much more. Unfortunately, none of the major browsers supports this functionality yet, although Lynx (a text-based browser) and iCab (a Macintosh browser) do, to some extent. For current use, the only reliable implementation of the link tag is to link external style sheet documents (see Chapter 11, "Using Cascading Style Sheets," for more on this).

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