Tag HTML in general is made couple, there is tag introduction and there are tag cover?conclusion. Public format tag HTML is :
< name_tag> Text which will be presented < /name_tag>
An example, for example this page heading applies tag header :
< h3> Is that tag HTML ? < /h3>
Tag will give information to web browser to present text " Is that tag HTML ?" with style header level 3. Tag HTML can instruct web browser to thicken a text ( bold), presents with format miring/italic, makes it as a header some levelly, or makes it as a hyperlink to other web page.
a tag cover?conclusion < /name_tag> always is given character " /", functioning to rif process tagging to web browser. Many tag HTML the always couple by the way of like this. If we forget gives tag cover?conclusion hence web browser will assume that tag tersebbut valids for overall of documents and result of the web page display not like the one is we wish.
Writing of tag-tag heedless HTML of letter usage ( case in-sensitive), will apply uppercase or lower case, will yield the same display.
Not as in programming language, mistake as result of situating or usage of tag HTML will not result computer system to become hang or breakdown. The mistake will only cause at the web page display.
Web browser of course intentionally is designed ably recognizes and executes ' only ' some tag HTML from overall of tag standard W3C. If (there are) any tag HTML that is unknown in web page is being processed, web browser will disregard it is likely tag not exist.
Example : < mytag tag HTML ? < /h3>
will present the same display with < h3>What HTML tag? < /h3>. So tag < mytag> and < /mytag> at all disregarded by web browser.
Don't forget to read What Is HTML? ........