The difference between empty and isset

These two functions have not been very understanding, write a small program to deepen understanding!

<?PHP/** * isset-detects if variable is set * Returns TRUE if the variable exists, otherwise returns false** empty-checks if a variable is null * If the variable is a non-null or nonzero value, empty () returns Fals e**/$is _var= ' ';if(isset($is _var)) {    Echo"Variable exists!" <br/> ";} Else {    Echo"The variable does not exist!" <br/> ";}if(Empty($is _var)) {    Echo"The variable is empty!" <br/> ";} Else {    Echo"The variable is not empty!" <br/> ";}?>

Output Result:

Variable exists!
The variable is empty!

The difference between empty and isset