Square brackets make them an array when the form is posted.

eg:- <input type=”text” name=”key_name[]“>

<form>
   <input type="text" name="key_name[]">
   <input type="text" name="key_name[]">
   <input type="text" name="key_name[]">
   <input type="text" name="key_name[]">
   <input type="submit" name="submit">
</form>

The above form will return an array of length 4, with the element in the order of declaration.

After the form is Submitted the fields with a name like “key_name[]” will be converted into a numeric array named key_name.

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