Specifying a taskID only with length, without a startdate

[solarjoe]

Proposal

For a Gantt chart, Mermaid.js should allow to specify a taskID followed by a length, without a startdate.
Currently this is allowed:

<taskID>, <startDate>, <length>

but I would like to use

<taskID>, <length>

But if you want to introduce a taskID to set up a dependency at some point,
you have to introduce a startDate, even if it is not necessary.

See the following example. Say you have many tasks (task1...5) and at some point you discover that you
want to create a reference (a2) to another swim lane.
Even though start and end are fully known for all tasks, the syntax <taskID>, <startDate>, <length>
forces me to add a date which breaks the chart.

gantt
    title A Gantt Diagram
    dateFormat  YYYY-MM-DD
    section Section1
    A task           :a1, 2014-01-01, 30d
    Another task1     :after a1  , 20d
    Another task2     :20d
    Another task3     :20d
    Another task4     :20d
    Another task5     :20d
    Another task6     :a2, 20d
    Another task7     :20d

Example

No response

Screenshots

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