While [[CommonMark|00001008010500]] is a well-specified Markdown dialect, some useful elements are missing.
To be precise, these elements are also missing from the original Markdown proposal.

Therefore, Zettelstore allows its users to make a trade-off and provides a choice: use CommonMark for a Markdown syntax that will be useful in other Markdown-processing software, or use Extended CommonMark to make use of elements found in proprietary Markdown-processing software.
The first choice focuses on the [[longevity|00001002000000]] of stored zettel, together with better compatibility with other tools.
The second choice trades longevity for additional features beyond CommonMark.

Extended CommonMark is a strict superset of CommonMark.
Every element of CommonMark is also supported in Extended CommonMark.
Currently, Extended CommonMark extends CommonMark with strikethrough and tables.

=== Strikethrough

One or two tilde characters (""''~''"", U+007E) mark deleted text.
For example, ``abc ~~def~~ ghi ~jkl~`` is rendered in HTML as: ::{{00001008010801}}::{=example}.

As with regular CommonMark emphasis delimiters, a new paragraph causes strikethrough parsing to stop.
Three or more tildes do not create a strikethrough.

=== Tables

A table consists of a single header row, a delimiter row separating the header from the data, and zero or more data rows.

Each row consists of cells containing arbitrary text in which inline elements are parsed, separated by vertical bar characters (""''|''"", U+007C).
A leading and trailing vertical bar character is also recommended for clarity.
Spaces between vertical bar characters and cell content are trimmed.

The delimiter row consists of cells whose only content is hyphen-minus characters (""''-''"", U+002D), optionally preceded or followed by a colon character (""'':''"", U+003A), or both, to indicate left, right, or center column alignment.

For example:

```emark
| foo | bar |
| --- | --- |
| baz | bim |
```

will be rendered in HTML as:

:::example
{{{00001008010802}}}
:::

To show the effect of an alignment specification:

```emark
| foo     | bar  | baz | bim |
| ------- | :--- | :-: | --: |
| default | left | center | rightright |
| one     | twotwo  | three  |
| alpha   | beta | gamma  | delta | epsilon |
```

will be rendered in HTML as:

:::example
{{{00001008010803}}}
:::