1. "What keyboard key can I press to create a linefeed character on a Mac?"
Depends on the app. End-of-line delimiters (also known as Newline) are not really input by the keyboard. The app interprets a press of the Return or Enter key, inserting into the data what it believes to be appropriate.
In most text editors such as TextMate, JEdit, BBEdit, TextWrangler, etc. you specify in prefs what the end of character should be. Some setting like "Lines end in: " with a popup menu offering LineFeed, Carriage Return, both. An app might even offer some special Unicode characters meant explicitly for such use (that nobody uses unfortunately).
So, the upshot is: The user presses Return (or whatever) and the app inserts the particular octet(s) for a LineFeed, Carriage Return, both, etc.
2. "I was having some issues with 4D text fields that were getting pasted in HTML code from TextMate which was supposed to be putting in linefeeds."
Yes, sharing data between apps is almost always tricky. The programmer or user must set/manipulate the desired end-of-line delimiters either in the data source (TextMate here) or the sink (4D here).
Remember that computers are illiterate. Ultimately they know nothing about characters and text. They truly only understand numbers. What you think of as a file full of text is actually a file full of numbers. If an app reads that file and encounters a "10" (Linefeed), the app may choose to treat that octet as an end-of-line. Or that app may ignore each occurrence of 10, blissfully cruising along looking for an expected '13' (Carriage Return) on which to break lines. To really see what an app sees when it opens a file, to see octet-by-octet, open the file yourself using a hex editor such as HexFiend.
Believe it or not, the geek in me finds this kind of topic fascinating: human language vs computerized data, character sets, Unicode, etc. I have actually had a friend call me to discuss such topics as a cure for his insomnia. Don't even get me started on the lack of foresight of the early computer information folks in the `60s and `70s.
- Many text editors do not convert existing documents when you change the end-of-line prefs setting. Your setting might apply only to future new files.
- You can verify what is being used with a hex editor such as HexFiend.
- Some older Mac programs still default to Carriage Return for end-of-line rather than the Unix convention of linefeed.
- Some cross-platform development tools try to help by defaulting to the convention used on the computer at runtime. But this can cause confusion as it changes the behavior of your app depending on which computer a user uses. Usually you should hard-code a specific consistent end-of-line. Java and REALbasic switch defaults, and as I recall 4D does too at least in some circumstances.
Here's how to hard-code generating a linefeed in REALbasic: