The current version of Textastic requires iOS 11, but you should be able to purchase Textastic 7 on a device with iOS 11 installed and then attempt to download it from the Purchased tab in the App Store on your iOS 9 device. It should ask you if you want to download the last version that was compatible with your device - Textastic 6.3.2 supported iOS 9. 

It seems like the Select button isn't shown sometimes. In that case tap Cancel and then tap Open... again. Looks like an iOS bug. 

Currently, it's not possible to adjust the light height, sorry.

Please try the following to import an image from the photo library: 

• go to a directory in Local Files or iCloud
• tap on the "+" button in the bottom toolbar
• select "Image"
• pick an image from the photo library
• enter a file name
• tap "Done"

There's a read-only option in Textastic's settings that disables the keyboard so that you cannot modify a file. Please double-check that this setting is disabled.

Please try to select "PHP" as the syntax definition in the File Properties.

Yes, currently this is a two-step process. I'll consider letting you select a target directory when copying a file.

It is still on my todo list but didn't make it into version 7.0. I hope I can add it into one of the next versions.

Good point, this could certainly be improved.

This is not really related to the filtering. When you open a file from the list of files, it is opened in a transient tab, indicated by the italic title. When you then tap on another file, that file replaces the transient tab.

To make a tab stay when you open another file, tap on the file title or the pin button at the right side of the transient tab, or tap on the editor to bring up the keyboard.

This behavior is very similar to what you see in desktop editors such as Sublime Text, VS Code and Atom. It prevents you from opening too many tabs when browsing the files in a project.