Are there any rules how to build the diminutive?
I was reading this article on Duden's webpage and began wondering about the diminutive forms of "-lein" and "-chen". Duden points out that the diminutive form, as you know, is often more a Koseform rather than always indicating a reduction in size, etc. And it states that "-lein" originated in the south (where obviously we still find various forms of it, such as the Schwäbisch "-le" usw), but that today "-chen" tends to be more frequently used.
Now, I think grammar books do teach that "-lein" and "-chen" really are completely interchangeable. But aren't there some words that always show up using only one form or the other? If so, is that simply because of how the words have developed from common or practical usage, or are there some words that grammatically can only use "-lein" or "-chen" but not both?
I appreciate the discussion between Takkat and Jan with Takkat's earlier question here, and they seem to agree that there may be some words that prefer one form or the other, but I'd like a more definitive answer on whether it's grammatical or just practical, if anyone knows.