I cannot find the thread in which it is written that
past tense has a boundary and present perfect has no its boundaries.
It is not the title, it is a part of the explanation.
Please help me find the thread.
The best way to search is to use Google, rather than the site search in the top-right corner. When using Google, you need to specify the site you want the results to come from, using the
site: parameter. The following is a suitable search, although it should all be on one line and entered as a single string into the search box:
past tense has a boundary and present perfect has no its boundaries. site:english.stackexchange.com
That currently gets you four results, three for this question (which is available by various routes), and one which might be the post you want: Habitual activities within a limited period of time
If you know the exact phrase you're looking for, enclose that in quotation marks:
"past tense has a boundary" site:english.stackexchange.com
That won't find what you're looking for if the exact phrase doesn't appear in the post.