This feature is used to protect your files from being changed or removed by another users.
You can lock or unlock the file by clicking
     on the toolbar, or click  → .
    on the toolbar, or click  → .
  
The
     icon is located next to the title of the locked file in the
    Workspace
    panel and at the title of this file tab in the
    Content
    panel.
    icon is located next to the title of the locked file in the
    Workspace
    panel and at the title of this file tab in the
    Content
    panel.
  

Another users can open the locked files in the only-read format, but cannot edit, save, delete, move or rename them.
If you open the locked file with the WYSIWYG editor, you can edit its content, but the Save function is disabled.