Input to MediaWiki should be NFC-normalized UTF-8. MediaWiki may attempt to convert other input, but this may cause some operations (such as edits with MD5 checks) to fail.
Parameters that take multiple values are normally submitted with the values separated using the pipe character, e.g. param=value1|value2 or param=value1%7Cvalue2. If a value must contain the pipe character, use U+001F (Unit Separator) as the separator and prefix the value with U+001F, e.g. param=%1Fvalue1%1Fvalue2.
Some parameter types in API requests need further explanation: