What is the difference between scrletter and scrlttr2?

Question

I'm asking about scrletter vs scrlttr2 , because it has been suggested for me.

I know there is the huge doc about scrguien, but I do not have time to read that and want a quick summary of the main points.

See also: How to convert a scrlttr2 letter to scrletter?. I've split the questions, because although they are related, they are different questions.

Answer 1

There are some differences between the usage of class scrlttr2 or the combination of eg scrartcl with the package scrletter¹.

• With scrlttr2 Letter Class Option files (lco files) can be loaded as class options or by one of the macros \LoadLetterClassOption or \LoadLetterClassOptions. With package scrletter they must be loaded by \LoadLetterClassOption or \LoadLetterClassOptions.
• Package scrletter loads package scrlayer-scrpage and defines a new pair of page styles letter and plain.letter.
• Package scrletter defines \letterpagemark to provide the formatted page number for the letters.
• With scrlttr2 font elements title and subject are aliases for lettertitle and lettersubject, respectively.
• scrlttr2 uses fontsize=12pt by default. Package scrletter does not change the fontsize of the class. Note that the main KOMA-Script classes use fontsize=11pt by default.

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¹There is also an undocumented wrapper-class scrletter. It loads class scrartcl with font size 12pt and package scrletter.

Answer 2

https://ctan.org/pkg/scrletter?lang=en

says

Used in conjunction with one of the Koma-Script (scrartcl, scrreprt, scrbook) or standard classes (article, report, book), this package provides the features of the letter class scrlttr2.

scrletter is a package used as \usepackage{scrletter} typically used to give a standard article class document some features of a KOMA lettter.

Conversely scrlttr2 is a class, used as \documentclass{scrlttr2}

https://ctan.org/pkg/scrlttr2?lang=en

says

The class was designed ‘from scratch’ as a replacement for the standard LaTeX letter class.