// Source: https://github.com/WPTRT/code-examples/blob/master/customizer/sanitization-callbacks.php

/**
 * Sanitization: number_range 
 * Control: number, tel 
 * 
 * Sanitization callback for 'number' or 'tel' type text inputs. This 
 * callback sanitizes $input as an absolute integer within a defined 
 * min-max range.
 * 
 * @uses	absint()	https://developer.wordpress.org/reference/functions/absint/ 
 * @link	is_int()	http://php.net/manual/en/function.is-int.php
 */
function theme_slug_sanitize_number_range( $input ) {
	
	// Ensure input is an absolute integer
	$input = absint( $input );
	
	// Get the input attributes
	// associated with the setting
	$atts = $setting->manager->get_control( $setting->id )->input_attrs;
	
	// Get min 
	$min = ( isset( $atts['min'] ) ? $atts['min'] : $input );
	
	// Get max 
	$max = ( isset( $atts['max'] ) ? $atts['max'] : $input );
	
	// Get Step
	$step = ( isset( $atts['step'] ) ? $atts['step'] : 1 );
	
	// If the input is within the valid range, 
	// return it; otherwise, return the default
	return ( $min <= $input && $input <= $max && is_int( $input / $step ) ? $input : $setting->default );
}