What do the structures ~ど/~ども exactly mean? How are they used?
I have seen these structures in this site:
https://nihongonosensei.net/?p=7938
but I don't understand very well the explanation, apart from the fact that they supposedly mean ~しても, which can be translated differently depending on the type of sentence it is used, and that they were used mostly in old times.
On the other hand, looking at the examples:
(1) 押せど、押せど、新着メールなし。
(2) 待てど暮らせど連絡が来ない。
(3) 寝れども寝れども寝不足だ。
It seems to me that ~ど/~ども do not convey any ~しても meaning (although, however hard, etc.), but more like "doing an action again and again". Then, I would like to clear up the meaning and usage of ~ど/~ども.
Besides, about the examples, if possible, could you please tell me what do they exactly refer to? In which context would those sentences appear? For me, without further context, they don't seem to be ancient-flavoured sentences from old writings and classical literature (古文). If ~ど/~ども don't make too much sense in this kind of sentences, could you please give me an example where you have seen ~ど/~ども used?