diff --git a/readme.md b/readme.md
index 6f1da20..732cd46 100644
--- a/readme.md
+++ b/readme.md
@@ -38,97 +38,71 @@ add_action( 'after_setup_theme', 'custom_theme_setup' );
 
 
 ---
+### Function Reference
 
-#### tevkori_get_sizes( $id, $size, $args )
+#### wp_get_attachment_image_sizes( $size, $image_meta = null, $attachment_id = 0, $image_src = null )
 
-Returns a valid source size value for use in a 'sizes' attribute. The parameters include the ID of the image, the default size of the image, and an array or string containing of size information. The ID parameter is required. [Link](https://github.com/ResponsiveImagesCG/wp-tevko-responsive-images/blob/master/wp-tevko-responsive-images.php#L28)
+Create 'sizes' attribute value for an image.
 
-***Usage Example***
+**Return:** (string|bool) A valid source size value for use in a 'sizes' attribute or false.
 
-```
-<img src="myimg.png" sizes="<?php echo tevkori_get_sizes( 11, 'medium' ); ?>" >
-```
 
-By default, the sizes attribute will be declared as 100% of the viewport width when the viewport width is smaller than the width of the image, or to the width of the image itself when the viewport is larger than the image. In other words, this:
-
-`(max-width: {{image-width}}) 100vw, {{image-width}}`
+##### Parameters
 
-You can override those defaults by passing your own size values as set of arrays to the `$args` parameter.
+**$size** (array|string)
+Image size. Accepts any valid image size name ('thumbnail', 'medium', etc.), or an array of width and height values in pixels (in that order).
 
-*Example:*
+**$image_meta** (array)            (Optional) The image meta data as returned by 'wp_get_attachment_metadata()'.
 
-```
-$args = array(
-  'sizes' => array(
-    array(
-      'size_value' 	=> '10em',
-      'mq_value'		=> '60em',
-      'mq_name'			=> 'min-width'
-    ),
-    array(
-      'size_value' 	=> '20em',
-      'mq_value'		=> '30em',
-      'mq_name'			=> 'min-width'
-    ),
-    array(
-      'size_value'	=> 'calc(100vm - 30px)'
-    ),
-  )
-);
-
-$sizes = tevkori_get_sizes( $id, 'medium', $args );
-```
+**$attachment_id** (int)
+(Optional) Image attachment ID. Either `$image_meta` or `$attachment_id` is needed when using the image size name as argument for `$size`.
 
-Which would output a sizes value of:
-`(min-width: 60em) 10em, (min-width: 30em) 20em, calc(100vm - 30px)`
+**$image_src** (string)
+(Optional) The URL to the image file.
 
----
+##### Usage Example
 
-#### tevkori_get_sizes_string( $id, $size, $args)
+```
+<img src="myimg.png" sizes="<?php echo esc_attr( wp_get_attachment_image_sizes( 'medium' ) ); ?>" >
+```
 
-Returns A full 'sizes' attribute. The parameters include the ID of the image, the default size of the image, and an array or string containing of size information. The ID parameter is required.
+By default, the sizes attribute will be declared as 100% of the viewport width when the viewport width is smaller than the width of the image, or to the width of the image itself when the viewport is larger than the image. In other words, this:
 
-***Usage Example***
+`(max-width: {{image-width}}) 100vw, {{image-width}}`
 
-```
-<img src="myimg.png" <?php echo tevkori_get_sizes_string( 11, 'medium' ); ?> >
-```
+You can override those defaults by adding a filter to `wp_get_attachment_image_sizes`.
 
 ---
-#### tevkori_get_srcset_array( $id, $size )
 
-Returns an array of image source candidates for use in a 'srcset' attribute. The parameters include the ID of the image, the default size of the image, and An array of of srcset values. The ID parameter is required. [Link](https://github.com/ResponsiveImagesCG/wp-tevko-responsive-images/blob/master/wp-tevko-responsive-images.php#L132)
+#### wp_get_attachment_image_srcset( $attachment_id, $size = 'medium', $image_meta = null )
 
-***Usage Example***
+Retrieves the value for an image attachment's 'srcset' attribute.
 
-```
-$sources = tevkori_get_srcset_array( 11, 'medium' );
+**Return:** (string|bool) A 'srcset' value string or false.
 
-// Optionally remove a specific source from the srcset list.
-foreach( $sources as $key => $source ) {
-	if ( strpos( $source, '300w' ) ) {
-		unset( $s[$key] );
-	}
-}
+##### Parameters
 
-<img src="myimg.png" srcset="<?php implode( ', ', $sources ); ?>" >
-```
+**$attachment_id** (int)
+Image attachment ID.
 
----
+**$size** (array|string)
+Image size. Accepts any valid image size, or an array of width and height values in pixels (in that order). Default 'medium'.
 
-#### tevkori_get_srcset_string( $id, $size )
+**$image_meta** (array)
+(Optional) The image meta data as returned by 'wp_get_attachment_metadata()'.
 
-Returns A full 'srcset' attribute. The parameters include the ID of the image and its default size. The ID parameter is required. [Link](https://github.com/ResponsiveImagesCG/wp-tevko-responsive-images/blob/master/wp-tevko-responsive-images.php#L196)
 
-***Usage Example***
+##### Usage Example
 
 ```
-<img src="myimg.png" <?php echo tevkori_get_srcset_string( 11, 'medium' ); ?> >
+<img src="myimg.png" srcset="<?php echo esc_attr( wp_get_attachment_image_srcset( 11, 'medium' ) ); ?>" sizes="{{custom sizes attribute}}" >
 ```
 
-**Dependencies**
+---
+
+### Dependencies
 
-The only external dependency included in this plugin is [Picturefill](http://scottjehl.github.io/picturefill/) - v2.3.0. If you would like to remove Picturefill (see notes about [browser support](http://scottjehl.github.io/picturefill/#support)), add the following to your functions.php file:
+The only external dependency included in this plugin is [Picturefill](http://scottjehl.github.io/picturefill/) - v3.0.1. If you would like to remove Picturefill (see notes about [browser support](http://scottjehl.github.io/picturefill/#support)), add the following to your functions.php file:
 
     function mytheme_dequeue_scripts() {
       wp_dequeue_script('picturefill');