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11.7 Named Frame or Window Targets
Section 11.4.1, you can label a frame by adding the
name attribute to its
<frame> tag.[2] Once
named, the frame may become the destination display window for a
hypertext-linked document selected within a document displayed in
some other frame. You accomplish this redirection by adding the
special target attribute to the anchor that
references the document.
[2] The
id attribute provides the same unique labeling but
cannot be used for frame content redirection.
11.7.1 The target Attribute for the <a> Tag
If you include a target attribute within an
<a> tag, the browser loads and displays the
document named in the tag's href
attribute in a frame or window whose name matches
the target. If the named frame or window doesn't
exist, the browser opens a new window, gives it the specified label,
and loads the new document into that window. Once this process has
been completed, hypertext-linked documents can target the new window.
Targeted hypertext links make it easy to create effectivce
navigational tools. A simple table of contents document, for example,
might redirect documents into a separate window:
<h3>Table of Contents</h3>
<ul>
<li><a href=" target="view_window">Preface</a>
<li><a href=" target="view_window">Chapter 1</a>
<li><a href=" target="view_window">Chapter 2</a>
<li><a href=" target="view_window">Chapter 3</a>
</ul>
The first time the user selects one of the table of contents
hypertext links, the browser opens a new window, labels it
"view_window," and displays the
desired document's contents inside it. If the user
selects another link from the table of contents and the
"view_window" is still open, the
browser again loads the selected document into that window, replacing
the previous document.
Throughout the whole process, the window containing the table of
contents is accessible to the user. By clicking on a link in one
window, the user causes the contents of the other window to change.
Rather than opening an entirely new browser window, a more common use
of target is to direct hyperlink contents to one
or more frames in a <frameset> display or to
an inline <iframe> window. You might place
the table of contents into one frame of a two-frame document and use
the adjacent frame for display of the selected documents:
<frameset cols="150,*">
<frame src="2">
<frame src=" name="view_frame">
</frameset>
When the browser initially displays the two frames, the left frame
contains the table of contents, and the right frame contains the
Preface (see Figure 11-6).
Figure 11-6. Table of contents frame controls content of adjacent frame
When a user selects a link from the table of contents in the left
frame (for example, Chapter 1), the browser loads and displays the
associated document into the
"view_frame" frame on the right
side (Figure 11-7). As other links are selected, the
right frame's contents change, while the left frame
continuously makes the table of contents available to the user.
Figure 11-7. The contents of Chapter 1 are displayed in the adjacent frame
11.7.2 Special Targets
There are four reserved
target names for special document-redirection actions:
_blank
The browser always loads a
target="_blank" linked document into a newly
opened, unnamed window.
_self
This target value is the default for all
<a> tags that do not specify a target,
causing the target document to be loaded and displayed in the same
frame or window as the source document. This target is redundant and
unnecessary unless used in combination with the
target attribute in the
<base> tag in a document's
head (see Section 11.7.3).
_parent
This target causes the
document to be loaded into the parent window or frameset containing
the frame containing the hypertext reference. If the reference is in
a window or top-level frame, then it is equivalent to the target
_self.
A brief example may help clarify how this link works. Consider a link
in a frame that is part of a three-column frameset. This frameset, in
turn, is a row in the top-level frameset being displayed in the
browser window. This arrangement is shown in Figure 11-8.
If no target is specified for the hypertext link, it is loaded into
the containing frame. If a target of _parent is
specified, the document is loaded into the area occupied by the
three-column frameset containing the frame that contains the link.
_top
This target causes the document to be
loaded into the window containing the hypertext link, replacing any
frames currently displayed in the window.
Continuing with the frame hierarchy, as shown in Figure 11-8, using a target of _top
would remove all the contained frames and load the document into the
entire browser window.
Figure 11-8. Using special hypertext targets in nested frames and framesets
All four of these target values begin with the
underscore character. Any other window or target beginning with an
underscore is ignored by the browser, so don't use
the underscore as the first character of any frame
name or id you define in your
documents.
11.7.3 The <base> Default Target
It can be tedious to
specify a target for every hypertext link in your documents,
especially when most are targeted at the same window or frame. To
alleviate this problem, you can add a target
attribute to the <base> tag. [<base>]
The target attribute in the
<base> tag sets the default target for every
hypertext link in the current document that does not contain an
explicit target attribute. For example, in our
example table of contents document, almost every link causes the
document to be displayed in another window named
"view_frame." Rather than including
that target in each hypertext link, you should place the common
target in the table of contents's
<base> tag within its
<head>:
<head>
<title>Table of Contents</title>
<base target="view_frame">
</head>
<body>
<h3>Table of Contents</h3>
<ul>
<li><a href=">Preface</a></li>
<li><a href=">Chapter 1</a></li>
<li><a href=" >Chapter 2</a></li>
<li><a href=">Chapter 3</a></li>
</ul>
</body>
Notice that we don't include any other target
references in the list of hyperlinks, because the browser loads and
displays all the respective documents in the base target
"view_frame."
11.7.4 Traditional Link Behavior
Before the onset of frames, each time you selected a hyperlink, the
corresponding document replaced the contents of the browser window.
With frames, this behavior is modified so that the corresponding
document replaces the content of the referencing frame. This is often
not the desired behavior, and it can be disconcerting to people
browsing your documents.
For example, suppose you have arranged all of the documents on your
site to present themselves in three frames: a navigational frame at
the top of the browser window, a scrolling content frame in the
middle, and a feedback form at the bottom. You named the content
frame with the name attribute of the
<frame> tag in the top-level document for
your collection and used the target attribute of
the <base> tag in every document on your
site to ensure that all links are loaded into the center content
frame.
This arrangement works perfectly for all the documents on your site,
but what happens when a user selects a link that takes him to a
different site? The referenced document is still loaded into the
center content frame. Now the user is confronted by a document from
some other site, surrounded by your navigation and feedback
frames![3] Very
impolite.
Chapter 17 for
how to step out into the forefront when your pages happen to be on
the other end of a targetless hyperlink.
The solution is to make sure that every hypertext link that
references a remote document has a target of _top.
This way, when the user selects a link that takes him away from your
site, the remote document replaces the contents of the entire browser
window, including your navigation and feedback frames. If the
majority of the links in your documents are to other sites, you might
consider adding target="_top" to a
<base> tag in your document and using
explicit target attributes in the links to your
local documents.
