The end-tag open (ETAGO) delimiter

1 · Mathias Bynens · June 10, 2011, 10:45 a.m.
According to HTML4, the first occurrence of the character sequence </ (ETAGO or end-tag open delimiter) is treated as terminating the end of the containing element’s content. This has since been changed in the HTML5 spec. What do browsers implement? How can we make sure the code we write doesn’t break because of this?...