Placing the mouse cursor over that sign will reveal the complete error description.
If you don't find any viruses or malware on your computer then try downloading the file again. You should download the latest version of HTML Validator and install it using the setup program.
W3C CSS based web application development has numerous benefits. This decreases the volume of visitors on your website. Another feature is that CSS created web pages are displayed in the same manner when these pages are viewed after downloading.
CSS is quite simple to discover from the regular open supply web sites.
The purpose behind introducing this language would be to present the different aspects and content of web page in presentable and sequence order. This only irritates the visitor and he browses to some other website from where he can access info with out any delay. W3C CSS enhances the appear of web pages and make them load quicker because it reduces the size of the web page by 60%.
HTML browsers are allowed to display HTML documents with errors (like missing end tags). A "well formed" XML document is not the same as a "valid" XML document. In addition, it must conform to a document type definition.