Object Names With Square Bracket

i want to update several Textboxes by reading the value of another Box. For that i use the following small script:

<form name="form1" method="POST">
<input type="text" name="xx" value ="1"

<input name="tex1" type="text" size=16 maxlength=80 value="1">
</form>

Everything works fine, but for my PHP-Script i need square brackets [
]. If i try to add them, my Script got an error:

<form name="form1" method="POST">
<input type="text" name="xx" value ="1"

<input name="tex[1]" type="text" size=16 maxlength=80 value="1">
</form>

Whats wrong?