English grammar/writing: use of "present perfect" as opposed to "past tense"

• https://en.wikipedia.org/wiki/Present_perfect#German
• https://en.wikipedia.org/wiki/Present_perfect#English
• https://en.wikipedia.org/wiki/Uses_of_English_verb_forms#Present_perfect

… . The choice of present perfect or past tense depends on the frame of reference (period or point in time) in which the event is conceived as occurring. … . If the frame of reference extends to the present time, the present perfect is used. … . If the frame of reference is a time in the past, or a period which ended in the past, the past tense is used instead. …

The use of present perfect resp. past tense is quite different (as described above [link]), and German native speakers confuse their use in English a lot; by my experience they rather resist accepting the difference and applying them properly in English. (This is rather annoying.)

English Writing: Spelling Rules - -ible or -able | EnglishClub.com

English Writing: Spelling Rules - -ible or -able | EnglishClub.com

English Writing: Spelling Rules – un- or in- – used with certain words to reverse their meaning

• un-
• in-

emphases in the English language

• adjectives get pronounced on their first syllable; e.g. …; counterexample: …
• verbs get pronounced on their second syllable; e.g. to refer, to access; counterexample: …
• nouns get pronounced on their first syllable; e.g. the access, …; counterexample: …

English grammar: commas and relative clauses

• "English in Use": Commas / Clarity
• "English in Use": Punctuation / Comma

Rule:

Relative that follows its antecedent:
When a relative (clause) immediately follows its antecedent, and is taken in a restrictive sense ("restrictive clause"), the comma should not be introduced before it.

The relative clause gets completed with a comma though. Of course it gets omitted, if there is a period anyway.

wikibooks on the grammar of the English language

• Subject:English language - Wikibooks, open books for an open world

Looks like the major entry in that list is this one:

• English in Use