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NOTE: This is a work in progress. Until it's finalized, this is NOT the official specification, which live elsewhere:
The current official and normative Gemini specification
In the same sense that HTML is the "native" response format of HTTP and plain text is the native response format of gopher, Gemini defines its own native response format - though of course, thanks to the inclusion of a MIME type in the response header Gemini can be used to serve plain text, rich text, HTML, Markdown, LaTeX, etc.
Response bodies of type "text/gemini" are a kind of lightweight hypertext format, which takes inspiration from gophermaps and from Markdown. The format permits richer typographic possibilities than the plain text of Gopher, but remains extremely easy to parse. The format is line-oriented, and a satisfactory rendering can be achieved with a single pass of a document, processing each line independently. As per gopher, links can only be displayed one per line, encouraging neat, list-like structure.
Similar to how the two-digit Gemini status codes were designed so that simple clients can function correctly while ignoring the second digit, the text/gemini format has been designed so that simple clients can ignore the more advanced features and still remain very usable.
As a subtype of the top-level media type "text", "text/gemini" inherits the "charset" parameter defined in RFC 2046. However, as noted in 3.3, the default value of "charset" is "UTF-8" for "text" content transferred via Gemini.
A single additional parameter specific to the "text/gemini" subtype is defined: the "lang" parameter. The value of "lang" denotes the natural language or language(s) in which the textual content of a "text/gemini" document is written. The presence of the "lang" parameter is optional. When the "lang" parameter is present, its interpretation is defined entirely by the client. For example, clients which use text-to-speech technology to make Gemini content accessible to visually impaired users may use the value of "lang" to improve pronunciation of content. When the "lang" parameter is not present, no default value should be assumed and clients which require some notion of a language in order to process the content (such as text-to-speech screen readers) should rely on user-input to determine how to proceed in the absence of a "lang" parameter.
Valid values for the "lang" parameter are comma-separated lists of one or more language tags as defined in RFC4646. For example:
As mentioned, the text/gemini format is line-oriented. Each line of a text/gemini document has a single "line type". It is possible to unambiguously determine a line's type purely by inspecting its first three characters. A line's type determines the manner in which it should be presented to the user. Any details of presentation or rendering associated with a particular line type are strictly limited in scope to that individual line.
There are 7 different line types in total. However, a fully functional and specification compliant Gemini client need only recognise and handle 4 of them - these are the "core line types", (see below). Advanced clients can also handle the additional "advanced line types" (see below). Simple clients can treat all advanced line types as equivalent to one of the core line types and still offer an adequate user experience.
The four core line types are:
Text lines are the most fundamental line type - any line which does not match the definition of another line type defined below defaults to being a text line. The majority of lines in a typical text/gemini document will be text lines.
Text lines should be presented to the user, after being wrapped to the appropriate width for the client's viewport (see below). Text lines may be presented to the user in a visually pleasing manner for general reading, the precise meaning of which is at the client's discretion. For example, variable width fonts may be used, spacing may be normalised, with spaces between sentences being made wider than spacing between words, and other such typographical niceties may be applied. Clients may permit users to customise the appearance of text lines by altering the font, font size, text and background colour, etc. Authors should not expect to exercise any control over the precise rendering of their text lines, only of their actual textual content. Content such as ASCII art, computer source code, etc. which may appear incorrectly when treated as such should be enclosed between preformatting toggle lines (see below).
Blank lines are instances of text lines and have no special meaning. They should be rendered individually as vertical blank space each time they occur. In this way they are analogous to <br/> tags in HTML. Consecutive blank lines should NOT be collapsed into a fewer blank lines. Note also that consecutive non-blank text lines do not form any kind of coherent unit or block such as a "paragraph": all text lines are independent entities.
Text lines which are longer than can fit on a client's display device SHOULD be "wrapped" to fit, i.e. long lines should be split (ideally at whitespace or at hyphens) into multiple consecutive lines of a device-appropriate width. This wrapping is applied to each line of text independently. Multiple consecutive lines which are shorter than the client's display device MUST NOT be combined into fewer, longer lines.
In order to take full advantage of this method of text formatting, authors of text/gemini content SHOULD avoid hard-wrapping to a specific fixed width, in contrast to the convention in Gopherspace where text is typically wrapped at 80 characters or fewer. Instead, text which should be displayed as a contiguous block should be written as a single long line. Most text editors can be configured to "soft-wrap", i.e. to write this kind of file while displaying the long lines wrapped at word boundaries to fit the author's display device.
Authors who insist on hard-wrapping their content MUST be aware that the content will display neatly on clients whose display device is as wide as the hard-wrapped length or wider, but will appear with irregular line widths on narrower clients.
Lines beginning with the two characters "=>" are link lines, which have the following syntax:
=>[<whitespace>]<URL>[<whitespace><USER-FRIENDLY LINK NAME>]
where:
All the following examples are valid link lines:
=> gemini://example.org/ => gemini://example.org/ An example link => gemini://example.org/foo Another example link at the same host => foo/bar/baz.txt A relative link => gopher://example.org:70/1 A gopher link
URLs in link lines must have reserved characters and spaces percent-encoded as per RFC 3986.
Note that link URLs may have schemes other than gemini. This means that Gemini documents can simply and elegantly link to documents hosted via other protocols, unlike gophermaps which can only link to non-gopher content via a non-standard adaptation of the `h` item-type.
Clients can present links to users in whatever fashion the client author wishes, however clients MUST NOT automatically make any network connections as part of displaying links whose scheme corresponds to a network protocol (e.g. links beginning with gemini://, gopher://, https://, ftp:// , etc.).
Any line whose first three characters are "```" (i.e. three consecutive back ticks with no leading whitespace) are preformatted toggle lines. These lines should NOT be included in the rendered output shown to the user. Instead, these lines toggle the parser between preformatted mode being "on" or "off". Preformatted mode should be "off" at the beginning of a document. The current status of preformatted mode is the only internal state a parser is required to maintain. When preformatted mode is "on", the usual rules for identifying line types are suspended, and all lines should be identified as preformatted text lines (see below).
Preformatting toggle lines can be thought of as analogous to <pre> and </pre> tags in HTML.
Any text following the leading "```" of a preformat toggle line which toggles preformatted mode on MAY be interpreted by the client as "alt text" pertaining to the preformatted text lines which follow the toggle line. Use of alt text is at the client's discretion, and simple clients may ignore it. Alt text is recommended for ASCII art or similar non-textual content which, for example, cannot be meaningfully understood when rendered through a screen reader or usefully indexed by a search engine. Alt text may also be used for computer source code to identify the programming language which advanced clients may use for syntax highlighting.
Any text following the leading "```" of a preformat toggle line which toggles preformatted mode off MUST be ignored by clients.
Preformatted text lines should be presented to the user in a "neutral", monowidth font without any alteration to whitespace or stylistic enhancements. Graphical clients should use scrolling mechanisms to present preformatted text lines which are longer than the client viewport, in preference to wrapping. In displaying preformatted text lines, clients should keep in mind applications like ASCII art and computer source code: in particular, source code in languages with significant whitespace (e.g. Python) should be able to be copied and pasted from the client into a file and interpreted/compiled without any problems arising from the client's manner of displaying them.
The following advanced line types MAY be recognised by advanced clients. Simple clients may treat them all as text lines as per "Text lines" above without any loss of essential function.
Lines beginning with "#" are heading lines. Heading lines consist of one, two or three consecutive "#" characters, followed by optional whitespace, followed by heading text. The number of # characters indicates the "level" of header; #, ## and ### can be thought of as analogous to <h1>, <h2> and <h3> in HTML.
Heading text should be presented to the user, and clients MAY use special formatting, e.g. a larger or bold font, to indicate its status as a header (simple clients may simply print the line, including its leading #s, without any styling at all). However, the main motivation for the definition of heading lines is not stylistic but to provide a machine-readable representation of the internal structure of the document. Advanced clients can use this information to, e.g. display an automatically generated and hierarchically formatted "table of contents" for a long document in a side-pane, allowing users to easily jump to specific sections without excessive scrolling. CMS-style tools automatically generating menus or Atom/RSS feeds for a directory of text/gemini files can use first heading in the file as a human-friendly title.
Lines beginning with "* " are unordered list items. This line type exists purely for stylistic reasons. The * may be replaced in advanced clients by a bullet symbol. Any text after the "* " should be presented to the user as if it were a text line, i.e. wrapped to fit the viewport and formatted "nicely". Advanced clients can take the space of the bullet symbol into account when wrapping long list items to ensure that all lines of text corresponding to the item are offset an equal distance from the edge of the screen.
Lines beginning with ">" are quote lines. This line type exists so that advanced clients may use distinct styling to convey to readers the important semantic information that certain text is being quoted from an external source. For example, when wrapping long lines to the the viewport, each resultant line may have a ">" symbol placed at the front.