WordPress File wp-includes/theme.php

switch_theme()

Switches the theme.

the_custom_header_markup()

Prints the markup for a custom header.

the_header_image_tag()

Displays the image markup for a custom header image.

the_header_video_url()

Displays header video URL.

unregister_default_headers()

Unregisters default headers.

validate_current_theme()

Checks that the active theme has the required files.

validate_theme_requirements()

Validates the theme requirements for WordPress version and PHP version.

wp_clean_themes_cache()

Clears the cache held by get_theme_roots() and WP_Theme.

wp_custom_css_cb()

Renders the Custom CSS style element.

wp_customize_support_script()

Prints a script to check whether or not the Customizer is supported, and apply either the no-customize-support or customize-support class to the body.