Descriptive "time blocks" in sequence diagrams

[kianhub]

Proposal

As an network analyst, I want to highlight a block of time in which certain messages are sent.

For timeline blocks I'd like to define the following within my sequence diagram to indicate a block that renders during which timeframe messages are sent.

Syntax proposal:
timeblock [arrow at start | arrow at end | arrows | line at start | line at end | lines]: [timeblock-title | empty]

Example

sequenceDiagram
        timeblock arrows Timeout
	HostA ->> HostB: Seq=92, 8 bytes data
	HostB --x HostA: ACK=100
	Note right of HostB: ACK is lost
	end
	HostA ->> HostB: Seq=92, 8 bytes data
	HostB ->> HostA: ACK=100
	Note left of HostA: SendBase = 100

The first message after a timeblock (displayed as two arrows vertically up and down, "timeout" in between) indicates the start of the timeblock while the first message after the end of a timeblock displays the end of it.

Screenshots