Source

File: wp-includes/user.php

function sanitize_user_field( $field, $value, $user_id, $context ) {
	$int_fields = array( 'ID' );
	if ( in_array( $field, $int_fields, true ) ) {
		$value = (int) $value;
	}

	if ( 'raw' === $context ) {
		return $value;
	}

	if ( ! is_string( $value ) && ! is_numeric( $value ) ) {
		return $value;
	}

	$prefixed = false !== strpos( $field, 'user_' );

	if ( 'edit' === $context ) {
		if ( $prefixed ) {

			/** This filter is documented in wp-includes/post.php */
			$value = apply_filters( "edit_{$field}", $value, $user_id );
		} else {

			/**
			 * Filters a user field value in the 'edit' context.
			 *
			 * The dynamic portion of the hook name, `$field`, refers to the prefixed user
			 * field being filtered, such as 'user_login', 'user_email', 'first_name', etc.
			 *
			 * @since 2.9.0
			 *
			 * @param mixed $value   Value of the prefixed user field.
			 * @param int   $user_id User ID.
			 */
			$value = apply_filters( "edit_user_{$field}", $value, $user_id );
		}

		if ( 'description' === $field ) {
			$value = esc_html( $value ); // textarea_escaped?
		} else {
			$value = esc_attr( $value );
		}
	} elseif ( 'db' === $context ) {
		if ( $prefixed ) {
			/** This filter is documented in wp-includes/post.php */
			$value = apply_filters( "pre_{$field}", $value );
		} else {

			/**
			 * Filters the value of a user field in the 'db' context.
			 *
			 * The dynamic portion of the hook name, `$field`, refers to the prefixed user
			 * field being filtered, such as 'user_login', 'user_email', 'first_name', etc.
			 *
			 * @since 2.9.0
			 *
			 * @param mixed $value Value of the prefixed user field.
			 */
			$value = apply_filters( "pre_user_{$field}", $value );
		}
	} else {
		// Use display filters by default.
		if ( $prefixed ) {

			/** This filter is documented in wp-includes/post.php */
			$value = apply_filters( "{$field}", $value, $user_id, $context );
		} else {

			/**
			 * Filters the value of a user field in a standard context.
			 *
			 * The dynamic portion of the hook name, `$field`, refers to the prefixed user
			 * field being filtered, such as 'user_login', 'user_email', 'first_name', etc.
			 *
			 * @since 2.9.0
			 *
			 * @param mixed  $value   The user object value to sanitize.
			 * @param int    $user_id User ID.
			 * @param string $context The context to filter within.
			 */
			$value = apply_filters( "user_{$field}", $value, $user_id, $context );
		}
	}

	if ( 'user_url' === $field ) {
		$value = esc_url( $value );
	}

	if ( 'attribute' === $context ) {
		$value = esc_attr( $value );
	} elseif ( 'js' === $context ) {
		$value = esc_js( $value );
	}
	return $value;
}