title: Encoding of Sz
role: manual
tags: #api #manual #reference #zettelstore
syntax: zmk
backward: 00001012920516 00001012931400 00001012931600
box-number: 1
copyright: (c) 2020-present by Detlef Stern <ds@zettelstore.de>
created: 20230403153903
forward: 00001006020000 00001007030000 00001007040000 00001007050000 00001012920516 00001012930000 00001012931200 00001012931400 00001012931600 00001012931800
lang: en
license: EUPL-1.2-or-later
modified: 20240123120319
published: 20240123120319
visibility: public

Zettel in a [[Sz encoding|00001012920516]] are represented as a [[symbolic expression|00001012930000]].
To process these symbolic expressions, you need to know, how a specific part of a zettel is represented by a symbolic expression.

Basically, each part of a zettel is represented as a list, often a nested list.
The first element of that list is always an unique symbol, which denotes that part.
The meaning / semantic of all other elements depend on that symbol.
=== Zettel
A full zettel is represented by a list of two elements.
The first elements represents the metadata, the second element represents the zettel content.
:::{="syntax"}
__Zettel__ **=** ''('' [[__Metadata__|#metadata]] [[__Content__|#content]] '')''.
:::
=== Metadata
Metadata is represented by a list, where the first element is the symbol ''META''.
Following elements represent each metadatum[^""Metadatum"" is used as the singular form of metadata.] of a zettel in standard order.

Standard order is: [[Title|00001006020000#title]], [[Role|00001006020000#role]], [[Tags|00001006020000#tags]], [[Syntax|00001006020000#syntax]], all other [[keys|00001006020000]] in alphabetic order.
:::{="syntax"}
__Metadata__ **=** ''(META'' [[__Metadatum__|00001012931200]] … '')''.
:::
=== Content
Zettel content is represented by a block.
:::{="syntax"}
__Content__ **=** [[__Block__|#block]].
:::
==== Block
A block is represented by a list with the symbol ''BLOCK'' as the first element.
All following elements represent a nested [[block-structured element|00001007030000]].
:::{="syntax"}
[!block|__Block__] **=** ''(BLOCK'' [[__BlockElement__|00001012931400]] … '')''.
:::
==== Inline
Both block-structured elements and some metadata values may contain [[inline-structured elements|00001007040000]].
Similar, inline-structured elements are represented as follows:
:::{="syntax"}
__Inline__ **=** ''(INLINE'' [[__InlineElement__|00001012931600]] … '')''.
:::
==== Attribute
[[Attributes|00001007050000]] may be specified for both block- and inline- structured elements.
Attributes are represented by the following schema.
:::{="syntax"}
__Attribute__ **=** ''('' **[** [[__AttributeKeyValue__|00001012931800]] … **]** ')'.
:::
Either, there are no attributes.
These are specified by the empty list ''()''.
Or there are attributes.
In this case, the first element of the list must be the symbol ''quote'': ''(quote'' ''('' A,,1,, A,,2,, … A,,n,, '')'''')''.
=== Other
A list with ''UNKNOWN'' as its first element signals an internal error during transforming a zettel into the Sz encoding.
It may be ignored, or it may produce an error.
:::{="syntax"}
__Unknown__ **=** ''(UNKNOWN'' Object … '')''.
:::
The list may only contain the symbol ''UNKNOWN'', or additionally an unlimited amount of other objects.

Similar, any symbol with the pattern ''**xyz:NOT-FOUND**'', where ''xyz'' is any string, signals an internal error.