Conventions:
All member variables that are prefixed with info
(including the main $info array) are used by HTML Purifier internals
and should not be directly edited when customizing the HTMLDefinition.
They can usually be set via configuration directives or custom
modules.
On the other hand, member variables without the info prefix are used
internally by the HTMLDefinition and MUST NOT be used by other HTML
Purifier internals. Many of them, however, are public, and may be
edited by userspace code to tweak the behavior of HTMLDefinition.