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-Goals:
-
-- no unicode (for efficient escaping, sightliness)
-- efficient operations for ACE and collab (attributed text, etc.)
-- good for time-slider
-- good for API
-- line-ending aware
-X more coherent (deleting or styling text merging with insertion)
-- server-side syntax highlighting?
-- unify author map with attribute pool
-- unify attributed text with changeset rep
-- not: reversible
-- force final newline of document to be preserved
-
-- Unicode bad:
- - ugly (hard to read)
- - more complex to parse
- - harder to store and transmit correctly
- - doesn't save all that much space anyway
- - blows up in size when string-escaped
- - embarrassing for API
-
-
-# Attributes:
-
-An "attribute" is a (key,value) pair such as (author,abc123456) or
-(bold,true). Sometimes an attribute is treated as an instruction to
-add that attribute, in which case an empty value means to remove it.
-So (bold,) removes the "bold" attribute. Attributes are interned and
-given numeric IDs, so the number "6" could represent "(bold,true)",
-for example. This mapping is stored in an attribute "pool" which may
-be shared by multiple changesets.
-
-Entries in the pool must be unique, so that attributes can be compared
-by their IDs. Attribute names cannot contain commas.
-
-A changeset looks something like the following:
-
-Z:5g>1|5=2p=v*4*5+1$x
-
-With the corresponding pool containing these entries:
-
-...
-4 -> (author,1059348573)
-5 -> (bold,true)
-...
-
-This changeset, together with the pool, represents inserting
-a bold letter "x" into the middle of a line. The string consists of:
-
-- a letter Z (the "magic character" and format version identifier)
-- a series of opcodes (punctuation) and numeric values in base 36 (the
- alphanumerics)
-- a dollar sign ($)
-- a string of characters used by insertion operations (the "char bank")
-
-If we separate out the operations and convert the numbers to base 10, we get:
-
-Z :196 >1 |5=97 =31 *4 *5 +1 $"x"
-
-Here are descriptions of the operations, where capital letters are variables:
-
-":N" : Source text has length N (must be first op)
-">N" : Final text is N (positive) characters longer than source text (must be second op)
-"<N" : Final text is N (positive) characters shorter than source text (must be second op)
-">0" : Final text is same length as source text
-"+N" : Insert N characters from the bank, none of them newlines
-"-N" : Skip over (delete) N characters from the source text, none of them newlines
-"=N" : Keep N characters from the source text, none of them newlines
-"|L+N" : Insert N characters from the source text, containing L newlines. The last
- character inserted MUST be a newline, but not the (new) document's final newline.
-"|L-N" : Delete N characters from the source text, containing L newlines. The last
- character inserted MUST be a newline, but not the (old) document's final newline.
-"|L=N" : Keep N characters from the source text, containing L newlines. The last character
- kept MUST be a newline, and the final newline of the document is allowed.
-"*I" : Apply attribute I from the pool to the following +, =, |+, or |= command.
- In other words, any number of * ops can come before a +, =, or | but not
- between a | and the corresponding + or =.
- If +, text is inserted having this attribute. If =, text is kept but with
- the attribute applied as an attribute addition or removal.
- Consecutive attributes must be sorted lexically by (key,value) with key
- and value taken as strings. It's illegal to have duplicate keys
- for (key,value) pairs that apply to the same text. It's illegal to
- have an empty value for a key in the case of an insertion (+), the
- pair should just be omitted.
-
-Characters from the source text that aren't accounted for are assumed to be kept
-with the same attributes.
-
-Additional Constraints:
-
-- Consecutive +, -, and = ops of the same type that could be combined are not allowed.
- Whether combination is possible depends on the attributes of the ops and whether
- each is multiline or not. For example, two multiline deletions can never be
- consecutive, nor can any insertion come after a non-multiline insertion with the
- same attributes.
-- "No-op" ops are not allowed, such as deleting 0 characters. However, attribute
- applications that don't have any effect are allowed.
-- Characters at the end of the source text cannot be explicitly kept with no changes;
- if the change doesn't affect the last N characters, those "keep" ops must be left off.
-- In any consecutive sequence of insertions (+) and deletions (-) with no keeps (=),
- the deletions must come before the insertions.
-- The document text before and after will always end with a newline. This policy avoids
- a lot of special-casing of the end of the document. If a final newline is
- always added when importing text and removed when exporting text, then the
- changeset representation can be used to process text files that may or may not
- have a final newline.
-
-Attribution string:
-
-An "attribution string" is a series of inserts with no deletions or keeps.
-For example, "*3+8|1+5" describes the attributes of a string of length 13,
-where the first 8 chars have attribute 3 and the next 5 chars have no
-attributes, with the last of these 5 chars being a newline. Constraints
-apply similar to those affecting changesets, but the restriction about
-the final newline of the new document being added doesn't apply.
-
-Attributes in an attribution string cannot be empty, like "(bold,)", they should
-instead be absent.
-
-
-
-
-
--------
-Considerations:
-
-- composing changesets/attributions with different pools
-- generalizing "applyToAttribution" to make "mutateAttributionLines" and "compose"