When and How to use ’ー’　in katakana? たとえば、リーダー、メッセージ、タクシー？i know it shoud b pronunced longer,but HOW and WHEN? when and how to use ’ー’　in katakana? たとえば、リーダー、メッセージ、タクシー？i know it should be pronunced longer, but HOW and WHEN to use it? can i simply use it as i wish...or does it have any specific rules for using 'ー'？for example, can i write 'leader' in リーダー、without 'ー'　so, can it just be リダ? It is really hard for me to ask this, i have asked this plenty of times, but seems like i still don't get the answer, (or maybe it is my mistake for not knowing what and how to ask) じゃ、anyone...よろしくお願いします！！ありがとう！