title: Encoding of Sz role: manual tags: #api #manual #reference #zettelstore syntax: zmk backward: 00001012920516 box-number: 1 copyright: (c) 2020-present by Detlef Stern created: 20230403153903 forward: 00001006020000 00001007030000 00001007040000 00001007050000 00001012920516 00001012930000 00001012931200 00001012931400 00001012931600 00001012931800 lang: en license: EUPL-1.2-or-later modified: 20260612185204 published: 20260612185204 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 a 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 element represents the metadata, the second element represents the zettel content. *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 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. *Metadata* __=__ `(META` [*Metadatum*](00001012931200) … `)`. # Content Zettel content is represented by a block. *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). *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: *Inline* __=__ `(INLINE` [*InlineElement*](00001012931600) … `)`. ## Attribute [Attributes](00001007050000) may be specified for both block- and inline- structured elements. Attributes are represented by the following schema. *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` `(` A1 A2 … An `)``)`. # Other ## `UNKNOWN` 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 may result in an error. *Unknown* __=__ `(UNKNOWN` Object … `)`. The list may only contain the symbol `UNKNOWN`, or, in addition, an unlimited amount of other objects. ## `**xyz:NOT-FOUND**` Any symbol with the pattern `**xyz:NOT-FOUND**`, where “`xyz`” is any string, signals an internal error. ## `*SPLICE-NODES*` A list with `*SPLICE-NODES*` as its first element may occur during internal processing. It signals that some processing routine intends to return more than one object instead of just one [*BlockElement*](00001012931400) or one [*InlineElement*](00001012931600). The elements of such a list should be “spliced” into the parent list. ## NIL (or `()`) Analogous to a splice node, which signals that more than one values is about to be returned, a “NIL” value (denoted as “`()`”) signals that no object should be returned. Therefore, a [*BlockElement*](00001012931400) or an [*InlineElement*](00001012931600) may be “NIL”.