Source

File: wp-admin/includes/theme-install.php

function install_theme_search_form( $type_selector = true ) {
	$type = isset( $_REQUEST['type'] ) ? wp_unslash( $_REQUEST['type'] ) : 'term';
	$term = isset( $_REQUEST['s'] ) ? wp_unslash( $_REQUEST['s'] ) : '';
	if ( ! $type_selector ) {
		echo '<p class="install-help">' . __( 'Search for themes by keyword.' ) . '</p>';
	}
	?>
<form id="search-themes" method="get">
	<input type="hidden" name="tab" value="search" />
	<?php if ( $type_selector ) : ?>
	<label class="screen-reader-text" for="typeselector"><?php _e( 'Type of search' ); ?></label>
	<select	name="type" id="typeselector">
	<option value="term" <?php selected( 'term', $type ); ?>><?php _e( 'Keyword' ); ?></option>
	<option value="author" <?php selected( 'author', $type ); ?>><?php _e( 'Author' ); ?></option>
	<option value="tag" <?php selected( 'tag', $type ); ?>><?php _ex( 'Tag', 'Theme Installer' ); ?></option>
	</select>
	<label class="screen-reader-text" for="s">
		<?php
		switch ( $type ) {
			case 'term':
				_e( 'Search by keyword' );
				break;
			case 'author':
				_e( 'Search by author' );
				break;
			case 'tag':
				_e( 'Search by tag' );
				break;
		}
		?>
	</label>
	<?php else : ?>
	<label class="screen-reader-text" for="s"><?php _e( 'Search by keyword' ); ?></label>
	<?php endif; ?>
	<input type="search" name="s" id="s" size="30" value="<?php echo esc_attr( $term ); ?>" autofocus="autofocus" />
	<?php submit_button( __( 'Search' ), '', 'search', false ); ?>
</form>
	<?php
}