I can't use this extension until Errors found while checking this document as XHTML 1.0 Transitional!
The part the module can break in terms of validation depends on what you put for the search URL parameter (usually "?option=com_search&searchword="). Note that the ampersand is not valid XHTML 1.0. If you have used Joomla before, you will have noted that the Joomla CMS formats any HTML entities in module parameters; if I put "?option=com_search&searchword=" then the second I save this in Joomla it changes it to "/?option=com_search&searchword=". Had you read the comments and queries on the documentation page you would know that my workaround of typing "?option=com_search&searchword=" was the solution to yours and many others validation issue. The default install sets this but Joomla CMS will reformat it everytime you save the parameter.
An honest rating but perhaps a bit harsh for a cloud word module especially since your issue is addressed on my site. Done correctly this module validates to XHTML 1.0 Strict but I haven't found a way to force Joomla CMS to stop formatting the entities.
Hope that helps!