Why is “ss” equal to the German sharp-s character 'ß'?

Question

Coming from this question I\'m wondering why ä and ae are different(which makes sense) but ß and ss are treated as equal.

Answer 1

Some background info for you. Taken from here.

Windows Alt Codes

In Windows, combinations of the ALT key plus a numeric code can be used to type a non-English character (accented letter or punctuation symbol) in any Windows application. More detailed instructions about typing accents with ALT keys are available. Additional options for entering accents in Windows are also listed in the Accents section of this Web site.

Note: The letters ü, ö, ä and ß can be replaced by "ue", "oe", "ae" or "ss" respectively.

German ALT Codes

Sym Windows ALT Code

Ä   ALT+0196
ä   ALT+0228
Ö   ALT+0214
ö   ALT+0246
Ü   ALT+0220
ü   ALT+0252
ß   ALT+0223
€   ALT+0128

Taken from here.

In the German alphabet, the letter ß, called "Eszett" (IPA: [ɛsˈtsɛt]) or "scharfes S", in English "sharp S", is a consonant that evolved as a ligature of "long s and z" (ſz) and "long s over round s" (ſs). When speaking it is pronounced [s] (see IPA). Since the German orthography reform of 1996, it is used only after long vowels and diphthongs, while ss is written after short vowels. The name eszett comes from the two letters S and Z as they are pronounced in German. It is also called scharfes S (IPA: [ˈʃaɐ̯.fəs ˈʔɛs, ˈʃaː.fəs ˈʔɛs] in German, meaning "sharp S". Its Unicode encoding is U+00DF.