mark up validation and xhtml

that particular error comes from the plugin ‘popupper-v10’:
this is line 113:

<script src="https://doublecheckmyhome.com/wp-content/plugins/popupper-v10/scripts/yui2.5.2_tooltip.js"></script>

assumingly, the plugin did not specify a ‘type’ such as:
<script type='text/javascript' src='htt.......

to get rid of the error message in the validation, you could edit the plugin, locate the code, and add the ‘type’

I appreciate your answer…

Please tell me how to get to

locate the source code

for the whole site to make the changes….

Thank you in advance

you might not be able to edit the plugin from your admin – editor.

because this error comes from a plugin, you need to open the plugin folder,
then open the ‘popupper-v10’ folder, and edit ‘popupper.php’:

in line 90 you should find:
echo '<script src="' . get_option('siteurl') . '/' . PLUGINDIR . '/popupper-v10/scripts/yui2.5.2_tooltip.js"></script>';

add the type="text/javascript" to it:
echo '<script type="text/javascript" src="' . get_option('siteurl') . '/' . PLUGINDIR . '/popupper-v10/scripts/yui2.5.2_tooltip.js"></script>';

and save the changes.

(in any case, a validation error like this is a minor error and will not lead to any misfunction of the code.)