linearLocation/associatedNetElement/@sequence shall be mandatory
## Background
2026-03-09 it was discussed at ETCS working group meeting that linearLocation/asscociatedNetElement/@sequence shall be mandatory because this info is always known.
## Links
* Forum discussion:
* Larissa Zhuchyi, 13.03.2026: https://www.railml.org/forum/index.php?t=msg&th=1134&start=0&
* Gitlab issues:
* #714
* #561
* #520
* Wiki documentation:
* RTM:associatedNetElement: https://wiki3.railml.org/wiki/RTM:associatedNetElement
## Suggested solution railML 3.4
`linearLocation/asscociatedNetElement/@sequence` shall be mandatory
issue