Offset Tracker

Offset tracking performs the function of tracking caret position in text across text transformation operations and during text editing.

As such there are some preparatory steps needed to aid the tracker in recovering the caret position accurately, especially after text transformation is applied immediately following an edit operation which results in the caret being surrounded by whitespace or format control characters such as LineSeparator (LS).

Caret surrounded by whitespace is problematic because most transformations do not preserve whitespace and may result in the text at the caret position to be removed. Additionally, typing spaces will result in them being collapsed after text wrapping, making it impossible to insert a space followed by non-space text after a word. It is more natural to allow one space behind the caret to remain even when there is one space after the caret already present to allow natural typing results.

Achieving this requires pre-processing the text and changing the first space after a word to   before applying text wrapping to prevent it from being collapsed with the next space and keeping the caret at the   character after wrapping.

The same applies to table formatting except all spaces before the caret, when caret is in the trailing whitespace region of a table cell and the cell, should be changed to   if a space was inserted before formatting the table. This has the effect of not collapsing any typed spaces in anticipation that a non-space will be typed. If on the other hand the caret is in the whitespace region before the cell text then no action is needed.

Similarly, if text is removed by a backspace operation the caret should be kept in the same relative position to the end of the previous word so it does not appear to jump around in the text as it is wrapped after the edit. If after backspace the caret was one or more spaces after of the previous word, then after wrapping it should be one space after the end of the word, even if the other spaces were collapsed or removed by having the following text wrap to the next line. This too is achieved by changing the space after the previous word to   before wrapping to allow it to survive the wrapping operation, and changing it back to a space after wrapping.

After backspace preparation of table text for formatting is the same as it is for space insert. Only the caret position relative to cell's text and cell alignment determine the required modification of text before applying table formatting.

Line Separator (LS) presents a special case because it will always be at the start of the next line after the text is wrapped. Text inserted right before the LS character will be wrapped to the previous line.

If the caret is immediately before the LS character or separated from it only by spaces, then typing will result in text appearing at the end of the previous line, instead of at the caret position. It is therefore desirable that the caret position be kept with the inserted text even if it is separated from it by a space than to keep it with the LS character on the next line.