Overwriting a text with spaces doesn't erase it.

How should I erase text ?

Here is my program:
(first you must use <Tools>/<Create Font...> to load the font)

//=================================
void setup() {
 size(120,120);
 noLoop();
 //
 PFont fontA;
 fontA = loadFont("dialog-12.vlw");
 textFont(fontA);
 //
 fill(0);
 text("aaaa", 5, 20);
 text("    ", 5, 20); //<< "aaaa" still there
 //
 for (int i=0; i<5; i++) text(str(i),60,20); //<< numbers overlap
 //
}

void draw() {
}
//=================================

Yes but I don't want to clear the whole screen.

So I should write a rectangle of background color over the text.
Here is the result:(not elegant but it works)

//======================================
void setup() {
 size(120,120);
 background(204);
 noLoop();
 //
 PFont fontA;
 fontA = loadFont("dialog-12.vlw");
 textFont(fontA);
 //
 fill(0);
 text("aaaa", 10, 20);// write text
 noStroke();
 fill(204,204,204);
 rect(10,20-12,textWidth("aaaa"),12);// erase text
 stroke(0);
 //
 fill(0);
 for (int i=0; i<3; i++) {
   noStroke();
   fill(204,204,204);
   rect(50,20-12,textWidth("0"),12);// erase previous num
   stroke(0);
   fill(0);
   text(str(i),50,20);// write num
 }
 //
}

void draw() {
}
//======================================