SlickEdit has the ability to display a thin vertical line at designated columns. This is helpful, for example, if you prefer to keep lines of code less than a certain width, or just as an additional visual guide.
The settings are under Tools > Options... > Appearance > General > "Vertical line columns" and "Vertical line color"
"Vertical line columns" is a list of numbers where you want vertical lines drawn. I like to use "80 132" to give me a visual guide of traditional terminal line widths. You can also customize the "Vertical line color", either on the Appearance > General form, or the Appearance > Colors form.
Vertical line columns work best for fixed width fonts, but they also work for proportional fonts, however, they are drawn at the position representing the column times an average character width. Still useful because it still gives you a visual guide for displayed line widths even though it is not a strict character count per line.
There is also an option for the "End" key to stop at vertical line columns. Tools > Options... > Keyboard and Mouse > Redefine Common Keys > Home/End behavior > End stops at vertical line column(s). This is helpful if you are trying to clean up text that has excessively long lines. You can hit "End", stop at column 80, move the the beginning of the word, and then split the line.
Albiet, this feature is a little bit old-school and not for everyone. Some will prefer to just let lines be as long as they need to be. Others like to use Soft Wrap for long lines. Others like to use Word Wrap to have long lines automatically split (not always great when programming though). Others only care about these features in HTML and comments, so they just use those specific word wrap options. To each his own.