Find some interesting HTML tags

I accidentally found some new HTML tags. I don't know which version I started from. Maybe I am falling behind. I only found them today.
First look at the effect:

Group

Group details

Group

Group details

Is it similar to the group component in winform?

Code Yes. < Fieldset Style = "Width: Auto" >
< Legend Style = "Color: # ff6600" > Group </ Legend >
Group details
</ Fieldset >  
< Fieldset Style = "Border-Right: Red 1px solid; border-top: Red 1px solid; border-left: Red 1px solid; width: auto; border-bottom: Red 1px solid" >
< Legend Style = "Color: # ff6600" > Group </ Legend >
Group details
</ Fieldset >