drupal7 如何在头部添加或删除一些meta ，html_head_alter

打开 html.tpl，你会发现  <?php print $head; ?>
如何改写这个 $head呢？

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首先，drupal_set_html_head 只在drupal6的，

在drupal7，只能用  drupal_add_html_head
https://api.drupal.org/api/drupal/includes%21common.inc/function/drupal_add_html_head/7
写法：function yourtheme_preprocess_html(&$variables) {  //注意，必须是在preprocess_html下。不是preprocess_page
// First, we must set up an array
$element = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array('http-equiv' => 'X-UA-Compatible', 'content' => 'IE=edge,chrome=1'),
  );
drupal_add_html_head($element, 'chrome_frame');
}

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如果使用了metatag模块，那会产生一些keywords or description，那用drupal_add_html_head就会重复增加了，这时要用hook:
当然你也用hook_html_head_alter可以覆写它，在
https://api.drupal.org/api/drupal/modules%21system%21system.api.php/function/hook_html_head_alter/7
function yourtheme_html_head_alter(&$head_elements) {
  // Force the latest IE rendering engine and Google Chrome Frame.
  $head_elements['chrome_frame'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array('http-equiv' => 'X-UA-Compatible', 'content' => 'IE=edge,chrome=1'),
  );
}
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输出形式在：theme_html_tag 
https://api.drupal.org/api/drupal/includes%21theme.inc/function/theme_html_tag/7
覆写方式：<?php
function THEMENAME_preprocess_html_tag(&$variables) {
。。。
}

删除一些meta：
http://drupal.stackexchange.com/questions/588/remove-certain-meta-tags-in-drupal-7
How can I remove these tags from my pages in Drupal 7?

<link rel="shortlink" href=" .... " />
<meta name="Generator" content="Drupal 7 (http://drupal.org)" />
<link rel="canonical" href="...." />
Update: I have the code for template.php, which removes the generator and canonical tags.

function program_html_head_alter(&$head_elements) {
  unset($head_elements['system_meta_generator']);
  foreach ($head_elements as $key => $element) {
    if (isset($element['#attributes']['rel']) && $element['#attributes']['rel'] == 'canonical') {
      unset($head_elements[$key]); 
    }
  }
}

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这样，可以添加一些js或css，或seo: keywords or description.
seo可以用模块metatag