Set a placeholder for PMPro text, textarea, and number User Fields.

pmpro-user-fields-html-attributes-placeholder.php

<?php
/**
 * Set placeholder values for PMPro user fields.
 *
 * Supported field types: text, textarea, number.
 *
 * 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_html_attributes_placeholder() {
	global $pmpro_user_fields;

	// Set placeholder values for the fields. Format: 'field_name' => 'placeholder value'
	$placeholder = array(
		'example_text'     => 'Enter text here.',
		'example_textarea' => 'Row one.' . "\r\n" . 'Row two.' . "\r\n" . 'Row three.',
		'example_number'   => '123',
	);

	// Loop through the fields and set the html_attributes array values.
	foreach ( $pmpro_user_fields as $field_group => $fields ) {
		foreach ( $fields as $field ) {
			// Bail if field type is not supported.
			if ( ! in_array( $field->type, array( 'text', 'textarea', 'number' ), true ) ) {
				continue;
			}
			if ( isset( $placeholder[ $field->name ] ) ) {

				// Bail if field value is set
				if ( ! empty( $field->value ) ) {
					continue;
				}

				// Bail if $placeholder is not a string.
				if ( ! is_string( $placeholder[ $field->name ] ) ) {
					continue;
				}

				// Remove html tags from string.
				$placeholder[ $field->name ] = wp_strip_all_tags( $placeholder[ $field->name ] );

				// remove all non-numbers from string if field type is number.
				if ( 'number' === $field->type ) {
					$placeholder[ $field->name ] = preg_replace( '/[^0-9]/', '', $placeholder[ $field->name ] );
				}

				// Set placeholder value for html_attributes if it's not already set.
				if ( empty( $field->html_attributes['placeholder'] ) ) {
					$field->html_attributes['placeholder'] = esc_attr( $placeholder[ $field->name ] );
				}
			}
		}
	}
}
add_action( 'init', 'my_pmpro_user_fields_html_attributes_placeholder' );