By default, a [[TiddlyWiki on Node.js]] instance using a [[wiki folder|TiddlyWikiFolders]] will create new tiddler files by using the sanitised and disambiguated title as filename and write them to the wiki folder's `tiddlers/` directory. This can be overridden by mapping a path in the wiki's tiddlywiki.info file, using a `default-tiddler-location` property in the `config` object. All filepath operations are relative to this `$tw.boot.wikiTiddlersPath` internal javacript variable.
The default file extension of `.tid` is used for tiddlers that are missing the `type` field, or for tiddlers of type "text/vnd.tiddlywiki". Tidders of other types are saved according to their IMIE types (defined at boot startup). Both the logical path (directory and file name) and the file extension can be customized independently by creating optional tiddlers: [[$:/config/FileSystemPaths]] and [[$:/config/FileSystemExtensions]].
The logical path can be customised by creating a tiddler [[$:/config/FileSystemPaths]] containing one or more [[filter expressions|Filter Syntax]], each on a line of its own. Newly created tiddlers are matched to each filter in turn, and the first output of the first filter to produce any output is taken as a logical path to be used for the tiddler file. Tiddlers are also tested against the [[$:/config/FileSystemPaths]] on every save to disk, and if the logical path has changed a new file is created and the old file deleted.
Tiddlers are limited to being written to the [[wiki folder|TiddlyWikiFolders]]. Any error saving a tiddler to disk, with a logical path that does not start with the wiki folder's path the most common error, causes the filepath to be encoded via Javascript's `encodeURIComponent()` method and the tiddler is saved as this file in the wiki folder's `$tw.boot.wikiTiddlersPath` directory.
Logical paths do not include the file-on-disk's extension (see below), and they can use `/` or `\` as directory separator (when generating the physical path, this is replaced by the correct separator for the platform ~TiddlyWiki is running on). If none of the filters matches, the logical path is simply the title with all occurences of `/` replaced by `_` (for backwards compatibility).
In both cases, the characters `<>~:"\|?*^` are replaced by `_` in order to guarantee that the resulting path is legal on all supported platforms.
This will store newly created system tiddlers that are not drafts of other tiddlers in `tiddlers/_system` (after stripping the `$:/` prefix). Next, all drafts have the path seperator characters in their titles replaced by "_" and are stored in `tiddlers/drafts/`. Then tiddlers tagged [[task]] are stored in a subdirectory `tiddlers/mytasks/`. Finally, all tidders not tagged with "externalnote" will match the final `[!tag[externalnote]addprefix[wiki/]]` storing these in `/wiki/`. In this example, tiddlers tagged with "externalnote" have been imported using [[tiddlywiki.files Files|tiddlywiki.files_Files]] with an "isEditableFile" flag set to true, causing the server to remember their original file path.
Whenever a tiddler generates a $:/config/FileSystemPaths filter match, any `/` or `\` in the tiddler title is mapped to a path separator. With the above filters, the non-system, non-draft tiddler `some/thing/entirely/new` (with no tags) will be saved to `<wikiFolder>/tiddlers/wiki/some/thing/entirely/new.tid` (ie, the file `new.tid` in a directory called `entirely/`). Thus, $:/config/FileSystemPaths itself will end up in `tiddlers/_system/config/FileSystemPaths.tid` or `tiddlers\_system\config\FileSystemPaths.tid`, depending on the platform.
Normally, the file system extension of a tiddler on disk is determined by the existance of bad fields (multi-line fields other than the text field, fields that can be trimmed of spaces from the fron or back, etc), in which case the single-file ".json" tiddler-file format is used. If the tiddler does not have bad fields, then the `type` field is referenced to find a matching file-type. Tiddlywiki's boot engine defines a set of these tiddler-type to file-type relationships in the [[$:/boot/boot.js]] tiddler. Search for `// Add file extension information` to find the section of code that defines these relationships.
The file extension of individual tidders can be customised by creating a tiddler [[$:/config/FileSystemExtensions]] containing one or more [[filter expressions|Filter Syntax]], each on a line of its own. Newly created tiddlers are matched to each filter in turn, and the first output of the first filter to produce any output is taken as the file extension to be used for the tiddler file. Extensions should always start with a leading dot (see example). Tiddlers are also tested against the $:/config/FileSystemExtensions on every save to disk, and if the extension has changed a new file is created and the old file deleted. If no filter matches, the default extension is used.
Two special cases should be noted: Result of ".tid" will force the tiddler to be written to disk as a single-file text tiddler. A result of ".json" will force the tiddler to be written to disk as a single-file tiddler in json-format (a single tiddler fields object in an array), NOT as a tiddler of type "application/json". All other recognized file-types will be saved using their defined extention along with an acompanying *.meta file of the same name which describes all fields but the "text" field.
This will cause all tidders that have the tag ".txt" in their tags field to be saved at the filepath determined by the File System Paths filters, but with their text field saved as a *.txt file, and all other fields saved as a *.txt.meta file.
Next, all tiddlers that have the ".json" tag are saved as *.json single-file tiddlers. Finally, all tiddlers that have tag ".tid" are saved as single-file text tiddlers. If a tiddler matches none of the filters, the default extension determined by the tiddler's `type` field would be used.
