Continuous fractions in CAS

[pinkman]

I wanted to improve my knowledge about continuous fractions, to be able to compete with Gerson and Albert.
I noticed that the CAS of the Prime has the two functions dfc and dfc2f, really fun to use to simplify the comprehension of continuous fractions.

Well indeed it works well, ie. dfc(π) returns [3,7,15,1,292,1,1,1,2], and dfc2f([3,7,15,1,292,1,1,1,2]) returns 833719/265381, which is a good approximation for π (3.14159265358).

Let’s continue with sqrt(2)
dfc(sqrt(2)) returns [1,2,2,2,2,2,2,2,2,2,2,2,2,2,2] (good!) and dfc(sqrt(2),5) returns... [1,2,[2]]

Here are my questions!
1- What does this last result [1,2,[2]] mean? I guess it means “repeat 2 until the end of times”, but I just discover this syntax. And why isn’t it also the answer for dfc(sqrt(2)) (I let the default epsilon value in CAS params) ?
2- How can I create such an array? I tried to edit it manually: (shift) (5[]) (1) (right) (2) (shift) (5[]) but it doesn’t open new brackets. When I use an external editor, as simple as the Notes app of the Prime, I can textually create [1,2,[2]], and with the copy-paste function I can paste it in the CAS environnement.

Thanks!