Hello Roman, In general, using " in' " at the end of words normally ending in "ing" is used to indicate casual and informal speech in the USA principally, and would only be used in writing to quote what somebody is saying. You would never use it in official documents. I have two further comments - one is that in your example, "gonna'" (with an apostrophe at the end) is wrong. The word is "gonna". "I'm gonna do that". The second comment is that the apostrophe serves two purposes. 1. The " 's " indicates "belonging" or the genitive. For example: the boy's arm hurts, or the government's policies encourages tax evasion. 2. The apostrophe indicates missing letters. For example: I'm goin' for I'm going. The "g" was missing. The term I'm for I am. The "a" is missing. Even "three o'clock" is an abbreviation for "three of the clock".

This use of apostrophes is used to indicate that writer would elide (= the act of not saying a sound in a word or between two separate words) sounds in the word when speaking. All native speakers of English elide sounds when they speak. It is not something only Americans do, nor is it bad English. Look at the transcriptions and you'll see why the author used apostrophes: fishing: /fɪʃi:ŋ/ fɪshɪn': /fiʃɪn/ or /fiʃn/ loving /lʌvi:ŋ/ lovin' /lʌvɪn/ or /lʌvn/ filling /fɪli:ŋ/ fillin' /fɪlɪn/ or /fɪln/ Did you see the /i:ŋ/ -> /ɪn/ or /n/ change? That is what the ' indicates. We don't use apostrophe in gonna because we typically don't write it (the internet and SMS messages is different). It is exactly the same thing as 'do not' -> 'don't' but 'don't' is an official contraction in writing while gonna isn't. Feel free to use these when you're speaking in informal situations, but don't use them in writing or speaking in formal situations.

No, Roman, it's not advised to use those forms in official documents. In fact, no contractions are welcome in official documents. They are You are I am We have been Plus, those words with apostrofe are very informal, they are simply indicating that there's a letter or part of a word missing. Like in Don't = letter O missin I've = 'ha' missing Hope I've helped