Boolean values passed to content_tag?

In Rails 1.2.3, if I call content_tag('input', :type =>
'checkbox', :checked => true, :disabled => true), I get

    <input type="checkbox" checked="true" disabled="disabled">

I expected content_tag to handle all boolean values in the same way,
to give me:
    <input type="checkbox" checked="checked" disabled="disabled">

but instead content_tag_string only converts the "disabled",
"readonly", and "multiple" attributes. This seems rather fragile, as
it requires RAILS to track HTML.

Why not convert all 'true' values to match the attribute name, and
remove all 'false' values?