What on earth is a たる adjective?

I was trying to find a nice memorable compound for 宛 with the reading of "エン" as it seems to be a pretty uncommon reading. I found this word in edict 宛転たる with the part of speech tag "taru-adj". I have never encountered a "taru-adj" before and I was wondering if anyone else had some experience with them. How do they differ from your standard adjectives?
-taru adjectives are a small set of adjectives that describe adverbial properties, such as 宛転たる (moving smoothly), and 堂々たる (majestic). If I'm not mistaken they do not tend to act as predicates, but directly modify nouns "堂々たる屋敷" or act as adverbs using the suffix -と "宛転と滑った."

EDIT: Third line. aargh, and first line
Edited: 2007-10-06, 4:34 am
Thanks again!
Edited: 2007-10-06, 6:03 am
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Thanks for the explanation JimmySeal!
I used to wonder how to use "堂々たる" but didn't check it.
I had no idea it was some minor group of adjectives.