Add placeholder HTML attribute to PMPro user fields

my_pmpro_user_fields_add_html_attributes.php

<?php
/**
 * Add placeholder HTML attribute to PMPro user fields.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmpro_user_fields_add_placeholder( $field, $where ) {

	$placeholder = '';

	switch ( $field->name ) {
		case 'my_field':
			$placeholder = 'Placeholder for field named my_field';
			break;
		case 'another_field':
			$placeholder = 'Placeholder for field named another_field';
			break;
		case 'field_3':
			$placeholder = 'Placeholder for field named field_3';
			break;
	}

	if ( $placeholder ) {
		$field->html_attributes = array(
			'placeholder' => $placeholder,
		);
	}

	return $field;
}
add_filter( 'pmpro_add_user_field', 'my_pmpro_user_fields_add_placeholder', 10, 2 );