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<sect1 id="learning.view.placeholders.standard">
    <title>Standard Placeholders</title>

    <para>
        In the <link linkend="learning.view.placeholders.basics">previous section</link>, we learned
        about the <methodname>placeholder()</methodname> view helper, and how it can be used to
        aggregate custom content. In this section, we'll look at some of the concrete placeholders
        shipped with Zend Framework, and how you can use them to your advantage when creating
        complex composite layouts.
    </para>

    <para>
        Most of the shipped placeholders are for generating content for the
        <emphasis>&lt;head&gt;</emphasis> section of your layout content -- an area you typically
        cannot manipulate directly via your application view scripts, but one you may want to
        influence. As examples: you may want your title to contain certain content on every page,
        but specific content based on the controller and/or action; you may want to specify
        <acronym>CSS</acronym> files to load based on what section of the application you're in; you
        may need specific JavaScript scripts loaded at different times; or you may want to set the
        <emphasis>DocType</emphasis> declaration.
    </para>

    <para>
        Zend Framework ships with placeholder implementations for each of these situations, and
        several more.
    </para>

    <sect2 id="learning.view.placeholders.standard.doctype">
        <title>Setting the DocType</title>

        <para>
            <emphasis>DocType</emphasis> declarations are troublesome to memorize, and often
            essential to include in your document to ensure the browser properly renders your
            content. The <methodname>doctype()</methodname> view helper allows you to use simple
            string mnemonics to specify the desired <emphasis>DocType</emphasis>; additionally,
            other helpers will query the <methodname>doctype()</methodname> helper to ensure the
            output generated conforms with the requested <emphasis>DocType</emphasis>.
        </para>

        <para>
            As an example, if you want to use the <acronym>XHTML1</acronym> Strict
            <acronym>DTD</acronym>, you can simply specify:
        </para>

        <programlisting language="php"><![CDATA[
$this->doctype('XHTML1_STRICT');
]]></programlisting>

        <para>
            Among the other available mnemonics, you'll find these common types:
        </para>

        <variablelist>
            <varlistentry>
                <term>XHTML1_STRICT</term>

                <listitem>
                    <para>
                        <acronym>XHTML</acronym> 1.0 Strict
                    </para>
                </listitem>
            </varlistentry>

            <varlistentry>
                <term>XHTML1_TRANSITIONAL</term>

                <listitem>
                    <para>
                        <acronym>XHTML</acronym> 1.0 Transitional
                    </para>
                </listitem>
            </varlistentry>

            <varlistentry>
                <term>HTML4_STRICT</term>

                <listitem>
                    <para>
                        <acronym>HTML</acronym> 4.01 Strict
                    </para>
                </listitem>
            </varlistentry>

            <varlistentry>
                <term>HTML4_Loose</term>

                <listitem>
                    <para>
                        <acronym>HTML</acronym> 4.01 Loose
                    </para>
                </listitem>
            </varlistentry>

            <varlistentry>
                <term>HTML5</term>

                <listitem>
                    <para>
                        <acronym>HTML</acronym> 5
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>

        <para>
            You can assign the type and render the declaration in a single call:
        </para>

        <programlisting language="php"><![CDATA[
echo $this->doctype('XHTML1_STRICT');
]]></programlisting>

        <para>
            However, the better approach is to assign the type in your bootstrap, and then render it
            in your layout. Try adding the following to your bootstrap class:
        </para>

        <programlisting language="php"><![CDATA[
class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    protected function _initDocType()
    {
        $this->bootstrap('View');
        $view = $this->getResource('View');
        $view->doctype('XHTML1_STRICT');
    }
}
]]></programlisting>

        <para>
            Then, in your layout script, simply <methodname>echo()</methodname> the helper at the
            top of the file:
        </para>

        <programlisting language="php"><![CDATA[
<?php echo $this->doctype() ?>
<html>
    <!-- ... -->
]]></programlisting>

        <para>
            This will ensure that your DocType-aware view helpers render the appropriate markup,
            ensure that the type is set well before the layout is rendered, and provide a single
            location to change the DocType.
        </para>
    </sect2>

    <sect2 id="learning.view.placeholders.standard.head-title">
        <title>Specifying the Page Title</title>

        <para>
            Often, a site will include the site or business name as part of the page title, and
            then add additional information based on the location within the site. As an example,
            the <filename>zend.com</filename> website includes the string
            "<filename>Zend.com</filename>" on all pages, and the prepends information based on the
            page: "Zend Server - <filename>Zend.com</filename>". Within Zend Framework, the
            <methodname>headTitle()</methodname> view helper can help simplify this task.
        </para>

        <para>
            At its simplest, the <methodname>headTitle()</methodname> helper allows you to aggregate
            content for the <emphasis>&lt;title&gt;</emphasis> tag; when you echo it, it then
            assembles it based on the order in which segments are added. You can control the order
            using <methodname>prepend()</methodname> and <methodname>append()</methodname>, and
            provide a separator to use between segments using the
            <methodname>setSeparator()</methodname> method.
        </para>

        <para>
            Typically, you should specify any segments common to all pages in your bootstrap,
            similar to how we define the doctype. In this case, we'll define a
            <methodname>_initPlaceholders()</methodname> method for operating on all the various
            placeholders, and specify an initial title as well as a separator.
        </para>

        <programlisting language="php"><![CDATA[
class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    // ...

    protected function _initPlaceholders()
    {
        $this->bootstrap('View');
        $view = $this->getResource('View');
        $view->doctype('XHTML1_STRICT');

        // Set the initial title and separator:
        $view->headTitle('My Site')
             ->setSeparator(' :: ');
    }

    // ...
}
]]></programlisting>

        <para>
            Within a view script, we might want to add another segment:
        </para>

        <programlisting language="php"><![CDATA[
<?php $this->headTitle()->append('Some Page'); // place after other segments ?>
<?php $this->headTitle()->prepend('Some Page'); // place before ?>
]]></programlisting>

        <para>
            In our layout, we will simply echo the <methodname>headTitle()</methodname> helper:
        </para>

        <programlisting language="php"><![CDATA[
<?php echo $this->doctype() ?>
<html>
    <?php echo $this->headTitle() ?>
    <!-- ... -->
]]></programlisting>

        <para>
            This will generate the following output:
        </para>

        <programlisting language="html"><![CDATA[
<!-- If append() was used: -->
<title>My Site :: Some Page</title>

<!-- If prepend() was used: -->
<title>Some Page :: My Site</title>
]]></programlisting>
    </sect2>

    <sect2 id="learning.view.placeholders.standard.head-link">
        <title>Specifying Stylesheets with HeadLink</title>

        <para>
            Good <acronym>CSS</acronym> developers will often create a general stylesheet for
            sitewide styles, and individual stylesheets for specific sections or pages of the
            website, and load these latter conditionally so as to decrease the amount of data
            needing to be transferred on each request. The <methodname>headLink()</methodname>
            placeholder makes such conditional aggregation of stylesheets trivial within your
            application.
        </para>

        <para>
            To accomplish this, <methodname>headLink()</methodname> defines a number of "virtual"
            methods (via overloading) to make the process trivial. The ones we will be concerned
            with are <methodname>appendStylesheet()</methodname> and
            <methodname>prependStylesheet()</methodname>. Each takes up to four arguments,
            <varname>$href</varname> (the relative path to the stylesheet),
            <varname>$media</varname> (the <acronym>MIME</acronym> type, which defaults to
            "text/css"), <varname>$conditionalStylesheet</varname> (which can be used to specify a
            "condition" under which the stylesheet will be evaluated), and
            <varname>$extras</varname> (an associative array of key and value pairs, commonly used
            to specify a key for "media"). In most cases, you will only need to specify the first
            argument, the relative path to the stylesheet.
        </para>

        <para>
            In our example, we'll assume that all pages need to load the stylesheet located in
            "<filename>/styles/site.css</filename>" (relative to the document root); we'll specify
            this in our <methodname>_initPlaceholders()</methodname> bootstrap method.
        </para>

        <programlisting language="php"><![CDATA[
class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    // ...

    protected function _initPlaceholders()
    {
        $this->bootstrap('View');
        $view = $this->getResource('View');
        $view->doctype('XHTML1_STRICT');

        // Set the initial title and separator:
        $view->headTitle('My Site')
             ->setSeparator(' :: ');

        // Set the initial stylesheet:
        $view->headLink()->prependStylesheet('/styles/site.css');
    }

    // ...
}
]]></programlisting>

        <para>
            Later, in a controller or action-specific view script, we can add more stylesheets:
        </para>

        <programlisting language="php"><![CDATA[
<?php $this->headLink()->appendStylesheet('/styles/user-list.css') ?>
]]></programlisting>

        <para>
            Within our layout view script, once again, we simply echo the placeholder:
        </para>

        <programlisting language="php"><![CDATA[
<?php echo $this->doctype() ?>
<html>
    <?php echo $this->headTitle() ?>
    <?php echo $this->headLink() ?>
    <!-- ... -->
]]></programlisting>

        <para>
            This will generate the following output:
        </para>

        <programlisting language="html"><![CDATA[
<link rel="stylesheet" type="text/css" href="/styles/site.css" />
<link rel="stylesheet" type="text/css" href="/styles/user-list.css" />
]]></programlisting>
    </sect2>

    <sect2 id="learning.view.placeholders.standard.head-script">
        <title>Aggregating Scripts Using HeadScript</title>

        <para>
            Another common tactic to prevent long page load times is to only load JavaScript when
            necessary. That said, you may need several layers of scripts: perhaps one for
            progressively enhancing menus on the site, and another for page-specific content. In
            these situations, the <methodname>headScript()</methodname> helper presents a solution.
        </para>

        <para>
            Similar to the <methodname>headLink()</methodname> helper,
            <methodname>headScript()</methodname> provides the ability to append or prepend scripts
            to the collection, and then echo the entire set. It provides the flexibility to specify
            either script files themselves to load, or explicit JavaScript. You also have the option
            of capturing JavaScript via
            <methodname>captureStart()</methodname>/<methodname>captureEnd()</methodname>, which
            allows you to simply inline the JavaScript instead of requiring an additional call to
            your server.
        </para>

        <para>
            Also like <methodname>headLink()</methodname>, <methodname>headScript()</methodname>
            provides "virtual" methods via overloading as a convenience when specifying items to
            aggregate; common methods include <methodname>prependFile()</methodname>,
            <methodname>appendFile()</methodname>, <methodname>prependScript()</methodname>, and
            <methodname>appendScript()</methodname>. The first two allow you to specify files that
            will be referenced in a <emphasis>&lt;script&gt;</emphasis> tag's
            <varname>$src</varname> attribute; the latter two will take the content provided and
            render it as literal JavaScript within a <emphasis>&lt;script&gt;</emphasis> tag.
        </para>

        <para>
            In this example, we'll specify that a script, "<filename>/js/site.js</filename>" needs
            to be loaded on every page; we'll update our
            <methodname>_initPlaceholders()</methodname> bootstrap method to do this.
        </para>

        <programlisting language="php"><![CDATA[
class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    // ...

    protected function _initPlaceholders()
    {
        $this->bootstrap('View');
        $view = $this->getResource('View');
        $view->doctype('XHTML1_STRICT');

        // Set the initial title and separator:
        $view->headTitle('My Site')
             ->setSeparator(' :: ');

        // Set the initial stylesheet:
        $view->headLink()->prependStylesheet('/styles/site.css');

        // Set the initial JS to load:
        $view->headScript()->prependFile('/js/site.js');
    }

    // ...
}
]]></programlisting>

        <para>
            Within a view script, we might then add an extra script file to source, or capture some
            JavaScript to include in our document.
        </para>

        <programlisting language="php"><![CDATA[
<?php $this->headScript()->appendFile('/js/user-list.js') ?>
<?php $this->headScript()->captureStart() ?>
site = {
    baseUrl: "<?php echo $this->baseUrl() ?>"
};
<?php $this->headScript()->captureEnd() ?>
]]></programlisting>

        <para>
            Within our layout script, we then simply echo the placeholder, just as we have all the
            others:
        </para>

        <programlisting language="php"><![CDATA[
<?php echo $this->doctype() ?>
<html>
    <?php echo $this->headTitle() ?>
    <?php echo $this->headLink() ?>
    <?php echo $this->headScript() ?>
    <!-- ... -->
]]></programlisting>

        <para>
            This will generate the following output:
        </para>

        <programlisting language="html"><![CDATA[
<script type="text/javascript" src="/js/site.js"></script>
<script type="text/javascript" src="/js/user-list.js"></script>
<script type="text/javascript">
site = {
    baseUrl: "<?php echo $this->baseUrl() ?>"
};
</script>
]]></programlisting>

        <note>
            <title>InlineScript Variant</title>

            <para>
                Many browsers will often block display of a page until all scripts and stylesheets
                referenced in the <emphasis>&lt;head&gt;</emphasis> section have loaded. If you have
                a number of such directives, this can impact how soon somebody can start actually
                viewing the page.
            </para>

            <para>
                One way around this is to emit your <emphasis>&lt;script&gt;</emphasis> tags just
                prior to closing the <emphasis>&lt;body&gt;</emphasis> of your document. (This is a
                practice specifically recommend by the <ulink
                    url="http://developer.yahoo.com/yslow/">Y! Slow project</ulink>.)
            </para>

            <para>
                Zend Framework supports this in two different ways:
            </para>

            <itemizedlist>
                <listitem>
                    <para>
                        You can render your <methodname>headScript()</methodname> tag whereever you
                        like in your layout script; just because the title references "head" does
                        not mean it needs to be rendered in that location.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        Alternately, you may use the <methodname>inlineScript()</methodname> helper,
                        which is simply a variant on <methodname>headScript()</methodname>, and
                        retains the same behavior, but uses a separate registry.
                    </para>
                </listitem>
            </itemizedlist>
        </note>
    </sect2>
</sect1>
