[Plugin] EditMetaInEPUB3 - Manage legacy meta entries in the EPUB3 metadata

[BeckyEbook]

Updated: July 28, 2026
Current Version: 0.0.9
Status: Experimental
Plugin type: edit

Plugin icon:


How it works:
This plugin provides a simple editor for legacy EPUB2-style metadata entries stored in an EPUB3 package document as:

<meta name="..." content="..."/>

According to the EPUB3 specification, these legacy metadata entries are ignored by EPUB3 reading systems and are intentionally not editable in Sigil's built-in EPUB3 Metadata Editor. However, they are still preserved in EPUB3 files and are used by some third-party applications and workflows.

Instead of manually editing the OPF file, this plugin allows you to safely manage these legacy metadata entries through a dedicated table-based interface.

This plugin was inspired by a MobileRead discussion about editing legacy EPUB2-style metadata preserved inside EPUB3 package documents.

The plugin:

• Displays all legacy meta entries that use the name and content attributes.
• Allows adding, editing and removing legacy metadata entries.
• Ignores protected entries used internally by Sigil (such as cover).
• Preserves legacy metadata entries exactly as entered.
• Warns before closing the window if there are unsaved changes.
• Prints a concise diagnostic log to the plugin console.

Important:
This plugin only edits legacy metadata entries stored as:

<meta name="..." content="..."/>

It does not edit standard EPUB3 metadata (such as dc:title, dc:creator or meta property="..." entries), which are already supported by Sigil's built-in EPUB3 Metadata Editor.

Installation:
1. Select Manage Plugins from the Plugins menu. In the Manage Plugins dialog box, select Use Bundled Python, if it isn't already selected. (If your Sigil version doesn't have a Use Bundled Python option, click one of the Auto buttons to detect the path or Set to manually select the Python interpreter path.)
2. Click Add Plugin and select EditMetaInEPUB3_v0.X.Y.zip. This will install the plugin, which you can then run via Plugins > Edit > EditMetaInEPUB3.

Issues:
This plugin is intended for advanced users who understand the structure of EPUB metadata.

Only legacy meta name/content entries are modified. Existing EPUB3 metadata, Dublin Core elements and meta property entries remain untouched.

Please report bugs or suggestions in this thread.

OS Requirements:
Windows/Linux/OS X.
Tested on Windows 10 and 11 with Sigil 2.8.1. It should also work on Linux and macOS.
*** Linux users will have to make sure that the PySide6 module is present if it's not already. ***

Sigil Requirements:
Minimum version of Sigil: 1.0.0 [not tested]

Credits/Thanks:
KevinH – for encouraging this plugin idea.

License/Copying:
GNU LGPL Version 2 or Version 3 your choice. Any other license terms are only available directly from the author in writing.

The plugin is currently in the Experimental stage, so I’m looking forward to your feedback. If no issues or bug reports come up within the next week or two, I will mark the plugin as Stable.

[BeckyEbook]

(Reserved for future use)

[KevinH]

Added to the Sigil Plugin Index. Thank you!

[philja]

Installed and tested on MacBook Sigil 2.8.1 and Linux also 2.8.1 AppImage version. Superficial testing only, but the plugin works as defined.

The only thing I don't like is the behaviour on the MacBook when the plugin runner starts up on the desktop where Sigil is open, and then the window where the work is done flips to another desktop. But that's the same for all the edit plugins I've got, so it's not a fault of this new plugin - rather, it's a 'feature' of Mac. One that doesn't encourage me to do serious stuff on the Mac.

[KevinH]

I never see that on either of my Macs. Was a problem sometimes with the older Tk widget library but not with PySide6 so far.

Are you by chance telling macOS to open new apps on another Desktop/Workspace? Or maybe utilizing the Desktop tiling features that MacOS supports (but I personally hate).

[DiapDealer]

Curious if something like this would help avoid losing the gui widget on some machines:

my_widget.setWindowFlags(QtCore.Qt.WindowStaysOnTopHint)

placed just before:

my_widget.show()

There's also:

my_widget.setWindowFlags(QtCore.Qt.Tool)

Even though it doesn't seem to happen everywhere all the time, I think this behavior might have something to do with widgets that have no parent.

[BeckyEbook]

I tried adding:

editor.setWindowFlags(QtCore.Qt.Tool)

and tested it on Windows.

Unfortunately, it introduced an unwanted side effect. If I click on the Sigil main window while the plugin window is open, the plugin window disappears and I have no way to bring it back. Since it is a Qt.Tool window, it doesn't have its own taskbar button, so it becomes effectively inaccessible until the plugin is restarted.

With the current implementation, the plugin window has its own taskbar button on Windows, so even if it gets hidden behind Sigil, it can easily be restored.

I'll also test the suggested change on macOS, since I understand the behavior there may be different.

-----

However, if I use

editor.setWindowFlags(QtCore.Qt.WindowStaysOnTopHint)

the plugin window remains above all other windows system-wide, even after switching to another application, which is also not the behavior I'm looking for.

[DiapDealer]

Agreed. Neither of those options would be an acceptable solution.