"Portable bookmarks" are special text comments in the file. You can move or rename a file, and its portable bookmarks will remain intact (while "usual" bookmarks get lost if you move or rename a file, or if you delete SynWrite history file).
Such bookmarks are comments with special uppercase "NOTE" or "TODO" word at comment start.
|example for HTML||<!--NOTE: Text here -->|
|example for CSS||/*NOTE: Text here */|
|example for PHP||//TODO: Text here|
|example for files without lexer||(*NOTE: Text here *)|
To handle such bookmarks, use two commands in the "Bookmarks" menu: "Drop portable bookmark" and "Go to portable bookmark".