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README.md

ShareJS with text-formatted document type

Original project is Joseph Gentle's ShareJS

This branch adds data type for formatted text.

Operations on rich text

Document is of the next form:

[
    {
        t: "Bold fragment"
        params:
            bold: true
            font-size: 14
    },
    {
        t: "Italic fragment"
        params: {italic: true}
    }
]

T is a text field, common text operation are applied on this field. Params is a set of key-value pairs, only "insert" and "delete" operations are applied for them. All positions are measured from the start of document, not a start of fragment.

Available operations:

  • text insertion p: 9 # Text will be inserted before this position ti: "bold" # Text to insert params: # Params of the inserted text bold: true font-size: 14
  • text deletion p: 8 # Text will be deleted starting with this position td: "Fragment" # Text to delete (needed both to revert and check operation) params: {italic: true} # Params of deleted text (needed both to revert and check operation)
  • param insertion p: 5 # Param will be inserted for text starting with that position len: 4 # Number of symbols that will insert param paramsi: # Added param (one param per operation) font: 14
  • param deletion p: 5 # Param will be deleted starting with this position len: 4 # Number of symbols that will delete param paramsd: # Removed param (one param per operation) bold: true

Params insertion and params deletion are both params change operations. Transformations of text inseration and text deletion are obvious, their behavior is copied from text ShareJS type. Text insertion is not changed when transformed against params change - it does not insert or remove any params. Thus, simultaneous text insertion and params insertion can lead to a following situation: client1 and client2 have doc [{t: "discssion", params: {}}] client1 inserts u: {p: 4, t: "u"} client2 inserts bold param: {p: 0, len: 9, paramsi: {bold: true}} After transformations & application of operations they will both have:

[
    {
        t: "disc"
        params: {bold: true}
    },
    {
        t: "u"
        params: {}
    },
    {
        t: "ssion"
        params: {bold: true}
    }
]

Simple idea to transfrom text insertion against params change does not work in all possible cases. Params change when transformed against text insertion gets split into two operations if needed. Text deletion might be split in up to three operations when tranformed against params change. Text and positions stay unchanged, only params field gets changed. Params change when transformed against text deletion might change its pos and length. Params change isn't transformed against another params change if they operate on different params. If two operations do same action (set equal value or remove param) then one of them might be cut down, but the overall effect will remain unchanged. If operations set param to different values than one of the operations will be cut down if needed. Server cuts down already applied operation if favour of new. Client cuts down new operation if favour of applied one.

Check also google group about rich text formatting using OT here: http://groups.google.com/group/sharejs/browse_thread/thread/f973fd957e34448e

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