Are 1–9 usually features of informal English (I) or more formal English (F)? 1 exclamation marks (!) I 2 dashes (–) 3 missing words (Got your invite today) 4 direct questions (Can you email over some directions?) 5 capital letters (LOVE) 6 adding extra information after the end of the letter (PS) 7 indirect questions (I would appreciate it if you could ...) 8 specialised language (regarding) 9 underlining (a nightmare)

Analysis:

• 1 exclamation marks (!) - I (Informal)
• 2 dashes (–) - I (Informal)
• 3 missing words (Got your invite today) - I (Informal)
• 4 direct questions (Can you email over some directions?) - I (Informal)
• 5 capital letters (LOVE) - I (Informal)
• 6 adding extra information after the end of the letter (PS) - I (Informal)
• 7 indirect questions (I would appreciate it if you could ...) - F (Formal)
• 8 specialised language (regarding) - F (Formal)
• 9 underlining (a nightmare) - I (Informal)

Explanation: Features like exclamation marks, dashes, missing words, direct questions, capital letters for emphasis, and the use of abbreviations like 'PS' are characteristic of informal communication. Indirect questions and specialized language, on the other hand, are generally found in more formal contexts.