Just after sending my reply I think I could reproduce the problem: in landscape, the first three buttons didn't respond anymore for me. Looks like a glitch in the beta that is hopefully fixed in an update.

Hello,

I cannot reproduce the problem on my 11" iPad Pro running iOS 13 beta 3.

Pressing the tab key works on the on-screen keyboard itself and in the additional row of keys above the keyboard. It also works for me with an external keyboard.

Does a reboot help? If it doesn't, can you please send me a short video?

Here is another part of the docs with more details:

Numbers within strings are compared using numeric value, that is, Name2.txt< Name7.txt < Name25.txt.
Numeric comparison only applies to the numerals in the string, not other characters that would have meaning in a numeric representation such as a negative sign, a comma, or a decimal point.

Hello,

Textastic 8 now uses the same file name sorting as Finder. Here is a screenshot of Finder on macOS 10.14:

"06" is interpreted as the number 6, "7F" as 7, "08" as 8, "75" as 75. 

Textastic uses the API NSString.localizedStandardCompare. From the docs:

Compares strings as sorted by the Finder. This method should be used whenever file names or other strings are presented in lists and tables where Finder-like sorting is appropriate. The exact sorting behavior of this method is different under different locales and may be changed in future releases. This method uses the current locale.

The big advantage is that files like this now sort correctly:

file 8

file 9

file 10

file 11

Previously "file 10" and "file 11" would be shown before "file 8".

I'm sorry that this messes up your naming scheme. As a workaround, you can either add a number like "1" as a prefix to all file names or not mix numbers and letters in your naming scheme to get the correct sorting.

Yes, I totally understand what you mean. I plan to revamp the "+" button in Textastic to let you create a new, untitled text document.

Would it be ok if this always starts out as a plain text file (you can change the syntax in the File Properties popover) or should there be options for other kinds of files?

Textastic 8 will have an option to ask for the password when connecting to (S)FTP servers.

Textastic 8 will support ECDSA and Ed25519 SSH keys.

Textastic 8 will allow you to select any installed monospaced font. You can use apps like AnyFont or Apple Configurator 2 to install custom fonts.