PowerD.html - WHILE definition

Syntaxes:
```
  WHILE <exp>
    <statements>
  ENDWHILE

  WHILE <exp> DO <statements>     // see DO
```
While <exp> is true all <statements> are processed. If <exp> is false, loop leaves.
```
  WHILE <exp1>
    <statements1>
  ELSEWHILE <exp2>
    <statements2>
  ALWAYS
    <statements>
  ENDWHILE
```
If <exp1> is true, <statements1> are processed, if no <exp2> is tested and it the result is true <statements2> are processed. Then if atleast one of <exp1> and <exp2> is true <statements> are processed. Loop leaves when neither <exp1> nor <exp2> is true. Multiple ELSEWHILEs are allowed and ALWAYS can be left.
If You add 'N' after WHILE or ELSEWHILE, the result of contition will be negated:
```
  WHILE a<b
  ELSEWHILE a=0
```
is the same as
```
  WHILEN a>=b
  ELSEWHILEN a
```
Returning values:
WHILE loop can return list of values, just add the return list after ENDWHILE keyword:
```
  ENDWHILE <list>
```
Early exit:
EXIT/EXITIF keyword