sub element represents a subscript.
The first example, shows part of a statement in an electronics exam. There, the
sub element represents the subscript part of the resistance input/output variables. The
var element is properly used to wrap the variables.
<p>Find <var>R<sub>in</sub></var> and <var>R<sub>out</sub></var> of the Bipolar Junction Transistor.</p>
Find Rin and Rout of the Bipolar Junction Transistor.
Now, the author makes some notes about a mathematical problem presented elsewhere in the document. The
sub element is used to mark up the variable's subscripts.
<p>Being <var>X<sub>0</sub></var> greater that 0 we can conclude there's at least one possible solution for this equation.</p>
Being X0 greater that 0 we can conclude there's at least one possible solution for this equation.
For information about global attributes refer to this list of global attributes in HTML5.
For information about global events refer to this list of global events in HTML5.