如何在PHP中转义隐藏的表单值

I know these:

1. For HTML text : htmlentities() or htmlspecialchars()
   When outputting plain visible text within HTML para/div tags.

2. For URL-encoded values : urlencode()
   When sending data to a function in PHP that expects URL encoded values.

I dont know this:

2. For HTML form values : ??
   When outputting hidden data within HTML <input value="DATA"> tags.

Attribute values are HTML text. Use htmlspecialchars.