WordPress 默认隐藏了很多功能，我们可以通过 add_theme_support() 函数启用它们。该函数必须在主题的 functions.php 文件中调用，如果想通过钩子函数加载的话则必须使用 after_setup_theme 这个钩子，因为 init 对于一些功能来说，已经太迟了。该函数语法如下：

add_theme_support( string $feature )

$feature：字符串（必填）。将要添加的功能名称。

$args,…：混合（可选）。额外参数用以指定具体功能。

目前支持的功能参数主要有：

  • post-thumbnails：特色图片。
  • post-formats：文章形式。
  • html5：HTML5支持。
  • custom-logo：自定义网站Logo图标。
  • custom-header-uploads：顶部图像上传。
  • custom-header：自定义网站顶部内容。
  • custom-background：自定义网站背景内容。
  • title-tag：自动生成页面标题信息，需调用<?php wp_head();?>。
  • customize-selective-refresh-widgets：小部件选择性更新。
  • starter-content：内容初始化。
  • responsive-embeds：自适应嵌入内容。
  • align-wide：配置块编辑器宽对齐。
  • dark-editor-style：配置暗风格块编辑器。
  • disable-custom-colors：禁用快编辑器自定义颜色。
  • disable-custom-font-sizes：禁用快编辑器自定义字体大小。
  • editor-color-pallete：配置块编辑器调色板。
  • editor-font-sizes：配置块编辑器字体大小。
  • editor-styles：配置块编辑器样式。
  • wp-block-styles：启用默认块编辑器样式。

该函数定义在 wp-includes/theme.php 文件中，具体代码如下：

function add_theme_support( $feature ) {
global $_wp_theme_features;

if ( func_num_args() == 1 )
$args = true;
else
$args = array_slice( func_get_args(), 1 );

switch ( $feature ) {
case 'post-thumbnails':
// All post types are already supported.
if ( true === get_theme_support( 'post-thumbnails' ) ) {
return;
}

/*
* Merge post types with any that already declared their support
* for post thumbnails.
*/
if ( is_array( $args[0] ) && isset( $_wp_theme_features['post-thumbnails'] ) ) {
$args[0] = array_unique( array_merge( $_wp_theme_features['post-thumbnails'][0], $args[0] ) );
}

break;

case 'post-formats' :
if ( is_array( $args[0] ) ) {
$post_formats = get_post_format_slugs();
unset( $post_formats['standard'] );

$args[0] = array_intersect( $args[0], array_keys( $post_formats ) );
}
break;

case 'html5' :
// You can't just pass 'html5', you need to pass an array of types.
if ( empty( $args[0] ) ) {
// Build an array of types for back-compat.
$args = array( 0 => array( 'comment-list', 'comment-form', 'search-form' ) );
} elseif ( ! is_array( $args[0] ) ) {
_doing_it_wrong( "add_theme_support( 'html5' )", __( 'You need to pass an array of types.' ), '3.6.1' );
return false;
}

// Calling 'html5' again merges, rather than overwrites.
if ( isset( $_wp_theme_features['html5'] ) )
$args[0] = array_merge( $_wp_theme_features['html5'][0], $args[0] );
break;

case 'custom-logo':
if ( ! is_array( $args ) ) {
$args = array( 0 => array() );
}
$defaults = array(
'width' => null,
'height' => null,
'flex-width' => false,
'flex-height' => false,
'header-text' => '',
);
$args[0] = wp_parse_args( array_intersect_key( $args[0], $defaults ), $defaults );

// Allow full flexibility if no size is specified.
if ( is_null( $args[0]['width'] ) && is_null( $args[0]['height'] ) ) {
$args[0]['flex-width'] = true;
$args[0]['flex-height'] = true;
}
break;

case 'custom-header-uploads' :
return add_theme_support( 'custom-header', array( 'uploads' => true ) );

case 'custom-header' :
if ( ! is_array( $args ) )
$args = array( 0 => array() );

$defaults = array(
'default-image' => '',
'random-default' => false,
'width' => 0,
'height' => 0,
'flex-height' => false,
'flex-width' => false,
'default-text-color' => '',
'header-text' => true,
'uploads' => true,
'wp-head-callback' => '',
'admin-head-callback' => '',
'admin-preview-callback' => '',
'video' => false,
'video-active-callback' => 'is_front_page',
);

$jit = isset( $args[0]['__jit'] );
unset( $args[0]['__jit'] );

// Merge in data from previous add_theme_support() calls.
// The first value registered wins. (A child theme is set up first.)
if ( isset( $_wp_theme_features['custom-header'] ) )
$args[0] = wp_parse_args( $_wp_theme_features['custom-header'][0], $args[0] );

// Load in the defaults at the end, as we need to insure first one wins.
// This will cause all constants to be defined, as each arg will then be set to the default.
if ( $jit )
$args[0] = wp_parse_args( $args[0], $defaults );

// If a constant was defined, use that value. Otherwise, define the constant to ensure
// the constant is always accurate (and is not defined later, overriding our value).
// As stated above, the first value wins.
// Once we get to wp_loaded (just-in-time), define any constants we haven't already.
// Constants are lame. Don't reference them. This is just for backward compatibility.

if ( defined( 'NO_HEADER_TEXT' ) )
$args[0]['header-text'] = ! NO_HEADER_TEXT;
elseif ( isset( $args[0]['header-text'] ) )
define( 'NO_HEADER_TEXT', empty( $args[0]['header-text'] ) );

if ( defined( 'HEADER_IMAGE_WIDTH' ) )
$args[0]['width'] = (int) HEADER_IMAGE_WIDTH;
elseif ( isset( $args[0]['width'] ) )
define( 'HEADER_IMAGE_WIDTH', (int) $args[0]['width'] );

if ( defined( 'HEADER_IMAGE_HEIGHT' ) )
$args[0]['height'] = (int) HEADER_IMAGE_HEIGHT;
elseif ( isset( $args[0]['height'] ) )
define( 'HEADER_IMAGE_HEIGHT', (int) $args[0]['height'] );

if ( defined( 'HEADER_TEXTCOLOR' ) )
$args[0]['default-text-color'] = HEADER_TEXTCOLOR;
elseif ( isset( $args[0]['default-text-color'] ) )
define( 'HEADER_TEXTCOLOR', $args[0]['default-text-color'] );

if ( defined( 'HEADER_IMAGE' ) )
$args[0]['default-image'] = HEADER_IMAGE;
elseif ( isset( $args[0]['default-image'] ) )
define( 'HEADER_IMAGE', $args[0]['default-image'] );

if ( $jit && ! empty( $args[0]['default-image'] ) )
$args[0]['random-default'] = false;

// If headers are supported, and we still don't have a defined width or height,
// we have implicit flex sizes.
if ( $jit ) {
if ( empty( $args[0]['width'] ) && empty( $args[0]['flex-width'] ) )
$args[0]['flex-width'] = true;
if ( empty( $args[0]['height'] ) && empty( $args[0]['flex-height'] ) )
$args[0]['flex-height'] = true;
}

break;

case 'custom-background' :
if ( ! is_array( $args ) )
$args = array( 0 => array() );

$defaults = array(
'default-image' => '',
'default-preset' => 'default',
'default-position-x' => 'left',
'default-position-y' => 'top',
'default-size' => 'auto',
'default-repeat' => 'repeat',
'default-attachment' => 'scroll',
'default-color' => '',
'wp-head-callback' => '_custom_background_cb',
'admin-head-callback' => '',
'admin-preview-callback' => '',
);

$jit = isset( $args[0]['__jit'] );
unset( $args[0]['__jit'] );

// Merge in data from previous add_theme_support() calls. The first value registered wins.
if ( isset( $_wp_theme_features['custom-background'] ) )
$args[0] = wp_parse_args( $_wp_theme_features['custom-background'][0], $args[0] );

if ( $jit )
$args[0] = wp_parse_args( $args[0], $defaults );

if ( defined( 'BACKGROUND_COLOR' ) )
$args[0]['default-color'] = BACKGROUND_COLOR;
elseif ( isset( $args[0]['default-color'] ) || $jit )
define( 'BACKGROUND_COLOR', $args[0]['default-color'] );

if ( defined( 'BACKGROUND_IMAGE' ) )
$args[0]['default-image'] = BACKGROUND_IMAGE;
elseif ( isset( $args[0]['default-image'] ) || $jit )
define( 'BACKGROUND_IMAGE', $args[0]['default-image'] );

break;

// Ensure that 'title-tag' is accessible in the admin.
case 'title-tag' :
// Can be called in functions.php but must happen before wp_loaded, i.e. not in header.php.
if ( did_action( 'wp_loaded' ) ) {
/* translators: 1: Theme support 2: hook name */
_doing_it_wrong( "add_theme_support( 'title-tag' )", sprintf( __( 'Theme support for %1$s should be registered before the %2$s hook.' ),
'<code>title-tag</code>', '<code>wp_loaded</code>' ), '4.1.0' );

return false;
}
}

$_wp_theme_features[ $feature ] = $args;
}

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