By default, PHP displays error messages in a web page when an error occurs. These error messages can be helpful for debugging your code, as they provide information about the type and location of the error.

To display error messages in PHP, you can use the error_reporting() function to specify which types of errors should be reported, and the ini_set() function to specify how errors should be displayed.

Here is an example of how to display error messages in PHP:

ini_set('display_errors', 1);
error_reporting(E_ALL);

The ini_set() function sets the value of a configuration option, in this case display_errors, which controls whether error messages should be displayed. The error_reporting() function sets which types of errors should be reported. In this example, the E_ALL constant specifies that all errors and warnings should be reported.

By default, error messages are displayed in the web page as plain text. You can customize the appearance of error messages by setting the error_reporting and error_prepend_string and error_append_string configuration options.

Here is an example of how to customize the appearance of error messages:

ini_set('display_errors', 1);
ini_set('error_prepend_string', '<div style="color: red;">');
ini_set('error_append_string', '</div>');
error_reporting(E_ALL);