"Use a “safe” encoding for your page (such as ISO-8859-1) or otherwise verify that the content of inputted data to see if it valid (including if you use UTF-8).

"Use a “safe” encoding for your page (such as ISO-8859-1) or otherwise verify that the content of inputted data to see if it valid (including if you use UTF-8). This is because certain invalid character sequences can cause the next character(like < (!)) to be ignored in some encodings." Could anyone elaborate on this? What are the 'dangers' of UTF-8 exactly? The author suggests that certain UTF-8 characters can mess with the markup. How?