* @return string
		 */
		protected function add_class_to_img_tag( $image, $class )
		{
			if( false === strpos( $image, 'class=' ) )
			{
				$image = str_replace( '<img', '<img class="' . $class . '" ', $image );
			}
			else if( false !== strpos( $image, 'class="' ) )
			{
				$image = str_replace( 'class="', 'class="' . $class . ' ', $image );
			}
			else if( false !== strpos( $image, "class='" ) )
			{
				$image = str_replace( "class='", "class='" . $class . ' ', $image );
			}

			return $image;
		}

		/**
		 * Make sure that HTML is xxx="...." and mot xxx='.....' which is not recognized by WP:
		 *		- src
		 *		- height
		 *		- width
		 *
		 * @since 4.7.5.1
		 * @param string $image
		 * @return string
		 */
		protected function ensure_attr_enclosure( $image )
		{
			$attrs = array( 'src', 'height', 'width' );

			foreach( $attrs as $attr )
			{
				$match_attr = array();

				if( preg_match( "/{$attr}='([^']+)'/", $image, $match_attr ) )
				{
					$new_attr = $attr . '="' . $match_attr[1] . '"';

					$pos = strpos( $image, $match_attr[0] );

					if( false !== $pos )
					{
						$image = substr_replace( $image, $new_attr, $pos, strlen( $match_attr[0] ) );
					}
				}
			}

			return $image;
		}

		/**
		 * Build internal responsive groups
		 * Needed to display in backend only for user information
		 *
		 * @since 4.7.5.1
		 */
		protected function group_image_sizes()
		{
			$widths = array();
			$all = $this->base_images;

			foreach( $all as $sizes )
			{
				if( ! in_array( $sizes['width'], $widths ) )
				{
					$widths[] = $sizes['width'];
				}
			}

			sort( $widths );

			$groups = array();

			while( count( $widths ) > 0 )
			{
				$current_width = array_shift( $widths );

				do
				{
					$found = false;
					$height_key = '';

					foreach( $all as $name => $sizes )
					{
						if( $sizes['width'] == $current_width )
						{
							$height_key = $sizes['height'];
							$group_key = $current_width . '*' . $height_key;
							$groups[ $group_key ][ $name ] = $sizes;

							unset( $all[ $name ] );
							$found = true;
							break;
						}
					}

					if( ! $found )
					{
						break;
					}

					/**
					 * Check remaining for same aspect ratio
					 */
					foreach( $all as $name => $sizes )
					{
						if( wp_image_matches_ratio( $current_width, $height_key, $sizes['width'], $sizes['height'] ) )
						{
							$groups[ $group_key ][ $name ] = $sizes;
							unset( $all[ $name ] );
						}
					}

				} while ( $found );
			}

			$this->size_groups = array();

			foreach( $groups as $group => $images )
			{
				$widths = array();

				foreach( $images as $image )
				{
					if( ! in_array( $image['width'], $widths ) )
					{
						$widths[] = $image['width'];
					}
				}

				sort( $widths );

				while( count( $widths ) > 0 )
				{
					$current_width = array_shift( $widths );

					foreach( $images as $name => $sizes )
					{
						if( $sizes['width'] == $current_width )
						{
							$this->size_groups[ $group ][ $name ] = $sizes;
							unset( $images[ $name ] );
						}
					}
				}

			}

		}

		/**
		 * Prepare overview of used image sizes for theme options page
		 *
		 * @since 4.7.5.1
		 * @return string
		 */
		public function options_page_overview()
		{
			$html = '';

			foreach( $this->size_groups as $size_group => $sizes )
			{
				$html .= '<h3>' . $this->get_group_headline( $size_group ) . '</h3>';

				$html .= '<ul>';

				foreach( $sizes as $key => $image )
				{
					$info = $image['width'] . '*' . $image['height'];
					if( isset( $image['crop'] ) && true === $image['crop'] )
					{
						$info .= '  ' . __( '(cropped)', 'avia_framework' );
					}

					$info .= ' - ' . $this->get_image_key_info( $key );

					$html .= '<li>' . $info . '</li>';
				}

				$html .= '</ul>';
			}

			return $html;
		}

		/**
		 * Returns the string for the group headline.
		 * Calculates the aspect ratio or only width/height if one value is 0
		 *
		 * @since 4.7.5.1
		 * @param string $group
		 * @return string
		 */
		protected function get_group_headline( $group )
		{
			$headline = '';

			$sizes = explode( '*', $group );

			$w = isset( $sizes[0] ) ? (int) $sizes[0] : 0;
			$h = isset( $sizes[1] ) ? (int) $sizes[1] : 0;

			if( 0 == $h )
			{
				$headline .= __( 'Images keeping original aspect ratio', 'avia_framework' );
			}
			else if ( 0 == $w )
			{
				$headline .= __( 'Images keeping original aspect ratio', 'avia_framework' );
			}
			else
			{
				$gcd = $this->greatest_common_divisor( $w, $h );
				$w = (int) ( $w / $gcd );
				$h = (int) ( $h / $gcd );

				$headline .= sprintf( __( 'Images aspect ratio: %d : %d', 'avia_framework' ), $w, $h );
			}

			/**
			 *
			 * @since 4.7.5.1
			 * @param string $headline
			 * @param string $group
			 * @return string
			 */
			return apply_filters( 'avf_admin_image_group_headline', $headline, $group );
		}

		/**
		 * Return readable info for an image size key for options page
		 *
		 * @since 4.7.5.1
		 * @param string $image_key
		 * @return string
		 */
		protected function get_image_key_info( $image_key )
		{
			$info = '';

			$info .= ( array_key_exists( $image_key, $this->readable_img_sizes ) ) ? $this->readable_img_sizes[ $image_key ] : $image_key;

			$info .= '  (';

			if( array_key_exists( $image_key, $this->theme_images ) )
			{
				$info .= __( 'added by theme', 'avia_framework' );
			}
			else if( array_key_exists( $image_key, $this->plugin_images ) )
			{
				$info .= __( 'added by a plugin', 'avia_framework' );
			}
			else if( array_key_exists( $image_key, $this->wp_default_images ) )
			{
				$info .= __( 'WP default size', 'avia_framework' );
			}
			else
			{
				$info .= __( 'unknown', 'avia_framework' );
			}

			$info .= ')';

			/**
			 *
			 * @since 4.7.5.1
			 * @param string $info
			 * @param string $image_key
			 * @return string
			 */
			return apply_filters( 'avf_admin_image_key_info', $info, $image_key );
		}


		/**
		 * Calculates the value based on https://en.wikipedia.org/wiki/Greatest_common_divisor - euclid's algorithm
		 *
		 * @since 4.7.5.1
		 * @param int $a
		 * @param int $b
		 * @return int
		 */
		protected function greatest_common_divisor( $a, $b )
		{
			if( 0 == $a )
			{
				return abs( $b );
			}

			if( 0 == $b )
			{
				return abs( $a );
			}

			if( $a < $b )
			{
				$h = $a;
				$a = $b;
				$b = $h;
			}

			do
			{
				$h = $a % $b;
				$a = $b;
				$b = $h;
			} while ( $b != 0 );

			return abs( $a );
		}
	}

	/**
	 * Returns the main instance of av_responsive_images to prevent the need to use globals
	 *
	 * @since 4.7.5.1
	 * @param array|null $config
	 * @return av_responsive_images
	 */
	function Av_Responsive_Images( $config = array() )
	{
		return av_responsive_images::instance( $config );
	}

}
<br />
<b>Fatal error</b>:  Uncaught Error: Call to undefined function Av_Responsive_Images() in /home/payon/public_html/wp-content/themes/enfold/functions.php:240
Stack trace:
#0 /home/payon/public_html/wp-settings.php(591): include()
#1 /home/payon/public_html/wp-config.php(92): require_once('/home/payon/pub...')
#2 /home/payon/public_html/wp-load.php(50): require_once('/home/payon/pub...')
#3 /home/payon/public_html/wp-blog-header.php(13): require_once('/home/payon/pub...')
#4 /home/payon/public_html/index.php(17): require('/home/payon/pub...')
#5 {main}
  thrown in <b>/home/payon/public_html/wp-content/themes/enfold/functions.php</b> on line <b>240</b><br />