Валидатор ругается на readonly="true"

[Alex&R]

Подскажите, что не так, почему валидатор ругается на readonly="true"

value of attribute "readonly" cannot be "true"; must be one of "readonly"

				<td><input readonly="true" type="text" name="booking_date" value="11.02.201…

The value of the attribute is defined to be one of a list of possible values but in the document it contained something that is not allowed for that type of attribute. For instance, the “selected” attribute must be either minimized as “selected” or spelled out in full as “selected="selected"”; a value like “selected="true"” is not allowed.

[Vlad]

Напишите readonly="readonly"