[Feature Request] Synced Blocks (Page Transclusions)

# Feature Request: Synced Blocks (Page Transclusions)

## Is your feature request related to a problem? Please describe.

This feature request aims to meet the following objectives:
- Expand the market share of ownCloud Infinite Scale (oCIS) among end users.
- Increase the product value of a single oCIS instance.

The use case for this feature request is present in popular software such as Notion.

## Describe the solution you'd like

Develop an extension that let's users create synced blocks (page transclusions) within a document.

### Example: Notion

https://www.notion.so/help/synced-blocks

### Example: Obsidian

https://forum.obsidian.md/t/edit-transcluded-embedded-notes-blocks-in-place-likely-requires-wyswyg-first/15339 (+180)

### Definition: Transclusion

https://en.m.wikipedia.org/wiki/Transclusion

### Implementation

_This section provides an example of synced block behavior, but the implementation may not be optimal._

An extension defines a delineator and identifier used at the start and end of a synced block for a given file: This creates a synced block file that contains the content (that the given file references).

```md
# Title
# # Subtitle

This file contains an example of an synced block with the delineator "~~~".

~~~ ID
"This is content within the synced block.",
~~~ ID
```

The synced block file is created.

```md
~~~ ID
"This is content within the synced block.",
~~~ ID
```

When the synced block's delineator and identifier (~~~ ID) is added to another file, this Synced Block extension will autofill the synced block's content using the synced block file content reference. So updating a synced block on one file also updates every other file that references the synced block.

```csv
"This is a csv file used to clarify the example",
~~~ ID
"This is content within the synced block.",
~~~ ID
```

An export of the `csv` file contains the synced block content, but not it's delineator or identifier.

```csv
"This is a csv file used to clarify the example",
"This is content within the synced block.",
```

## Describe alternatives you've considered

- No Synced Block Feature: Copy and paste the synced content of every file every time synced content is updated.

# Resources

I am willing to develop the Synced Block extension on the following conditions:
- An optimal oCIS extension implementation is determined _(preferably by owncloud developers)_.
- An oCIS extension marketplace is released and stable.
- For [sponsorship](https://github.com/sponsors/switchupcb?frequency=one-time) or salary.

Otherwise, this feature request is published in an Open Source Software environment, available to all for implementation.