CHDIR pathname
 To let current-folder move to new 'pathname'.
 Currentp-folder is the folder working present.
 In the file specification of each command,
  when it is omitted specifying absolute path with "/"(root) at the beginning,
  it's judged as a file under current folder.
 By 'chdir' command, it's possible to move current folder
  to the location of "current-folder/pass-name" newly.(subordinate move)
 By description "../" of the beginning,
  it's possible to move to upper pass relatively.(multiple description OK)
   chdir "test"
   'move to "mnt/sdcard/and.bas/test/"
   chdir ".."
   'move to upper folder
   chdir "../txt"
   'move to upper folder, and move to lower "txt/".

 File system
  There are two basic current-folder to handle the file, the next.

  Specifying SD card side:
   /mnt/sdcard/    Android4.4
   /storage/emulated/0/Android/data/and.bas/files/    Android10 or later
  Startup subpath(followed behind the current-folder)
   and.bas/    Android4.4
   Android10 or later: The initial subpath is null.

  Specifying main storage side:
   /data/data/and.bas/    Android4.4
   /data/user/0/and.bas/files/    Android10 or later
  Startup subpath(followed behind the current-folder)
   files/    Android4.4
   Android10 or later: The initial subpath is null.

  When specifying SD card side and start-up,
  usually, it start from here.(and.bas/ is subpath)
   /mnt/sdcard/and.bas/    Android4.4
   /storage/emulated/0/Android/data/and.bas/files/    Android10以降の場合
  (Sometimes, there are different case by depend on the model,
   the majority of the models will be in this location)

  A part of this subpath can move by 'chdir' command.
  but can not go up to upper than current-folder.

  The 'mkdir' command can create a new folder.

  Key-assign state is saved main storage side.
  The current folder name can be acquired in 'curdir$()'.

  Save & load by command.

  When the head start with "/", it mean to have specified the full path.
   e.g.    load"/mnt/sdcard/my/test/file1.bas"  just described location.

  When non "/" beginning,
  it's judged as the path & file-name that it continue in present current-folder.
   e.g.    load"file1.bas" -> mnt/sdcard/and.bas/file1.bas  (judged as this)

  And, to refer to hierarchy upper, "../" can be used like DOS.(multiple OK)
   e.g.    load"../my/file1.bas" -> mnt/sdcard/my/file1.bas  (judged as this)
  (up to upper 'sdcard/' once, and down to 'my/')
  *The location without access permission can't be accessed.

 Load by dialog (Menu>Load)
  The file list is displayed, it can be loaded by touch & selection.
  When folder(sentence-end"/") is chosen, it will be in the folder movement.
  For move to hierarchy upper, chose '..'.

  When load file, it became that it have been 'chdir' to the location automatically,
  Current-folder is transferred to that location.
  *When finish dialog by back-button, load is not executed,
  Only current-folder move by 'chdir' is done.

  When chose 'New folder', it becomes text input mode for folder-name,
  A new folder can be made.

 Save by dialog (Menu>Save)
  It can input file name and save.
  It's saved in the location of the current-folder.
  By entering the path-name at the head,
  it can specify the path following a current.

  When want to specifiey the path of the hierarchy upper,
  Please put the "../" in the head,(multiple OK)

  File deletion management:
  Program 'filedel.bas' can do file deletion work in the current folder.
  (Selected one is deleted)
  (Not empty folder cann't be deleted)
  File name can also be changed by choosing 'Rename'.

 About models that SDcard cannot access by default.
 Android4.4 models usually cannot access the SDcard unless rooted.
 Some Android5.0-9.0 models with SDcard path type of UUID(xxxx-xxxx), it cannot access SDcard.
 These can access SDcard now as Current folder by the next operation.
 To create 'and.basf' folder under the following folder with FileExplorer App.
 For Android4.4 models:  /sdcard/Android/data/
 For Android5.0-9.0 models:  /storage/xxxx-xxxx/Android/data/
 After creating folder, and start Basic app, (load,save)access become possible at its location.
 Please note that this folder disappears when uninstall the app.