This addon places a highlighted border around various enemy buffs on the target and focus frames that your class is able to dispel, just like a mage sees a border around buffs he can spellsteal.
What does it look like?
In the default UI, it places a border around the dispellable buff. It is the same yellow border that is used to show which spells a mage can spellsteal.
Please look at the screenshots below for a better idea.
What features does it have?
The following options exist for both target and focus frames:
showing borders around dispellable buffs on enemies
enlarging these dispellable buffs on enemies for greater visibility (this is disabled by default)
enlarging spellstealable buffs on enemies for greater visibility (as a mage only, this is disabled by default)
What classes can dispel what?
Priests, shamans, warriors (prot), warlocks (fel hunters), and hunters can dispel magic buffs from enemies.
Hunters, rogues, and druids can dispel enrage buffs from enemies.
Mages can spellsteal most, but not all, magic buffs from enemies. Their ability to remove magic buffs from enemies is ignored in DispelBorder as the border functionality for spellstealing already exists (which is the basis of DispelBorder).
At what levels do classes learn the dispel/purge abilities?
I don't know. With the exception of shield slam, all are baseline at max level. It's much easier to just check for your class (and for warlocks and warriors, to check your pet or spec) and hope you as a player know what your dispel abilities are and if they are currently available.
Support for unitframe addons (like X-Perl, as opposed to the default UI):
If the unitframe addon shows spellstealable buffs somehow, dispellable enemy buffs will look the same (default UI: yellow border around it)
If the unitframe addon differentiates between spells cast by you and others, it will show "enlarged buffs" however it displays buffs cast by you (default UI: enlarged icons)
* Due to hooking UnitAura causing errors when clicking off buffs, it is no longer hooked by default. Only UnitBuff is hooked, which is what the default UI uses. Other addons that use UnitAura can try the "Hook UnitAura" option that is now available in the options panel.