Added an argument hint: inside a function's parentheses the autocomplete panel shows the syntax with the argument being typed in bold. A formula that cannot be read, such as =SUM(A1 with a missing parenthesis, is saved as entered and shows #ERROR!, and a message names what was expected and the character position. Formulas waiting for a later calculation pass show … instead of #ERROR!.
Added argument hints and a message for unreadable formulas in Spreadsheets
While typing inside a function, autocomplete shows its syntax with the current argument in bold. A formula that cannot be read is kept and a message names the position.