Disable pickup on a BLF

Usually it is quite useful to be able to pick up calls by pressing a fast blinking LED on your VoIP phone. This has become a standard feature on most IP-PBX today and practically all VoIP phones support this.
Sometimes there are however situations when you don't want this and instead the LED should just turn on without blinking, so that the user can see that the extension or resource is just busy. This can be a problem of permission, where users should not be able to pick up calls, e.g. on boss phones only certain extensions should be able to pick up that call.
A blinking LED is actually a "promise" that pressing the LED will pick up an incoming call. This was not always the case with the Vodia PBX. It could happen that the LED was blinking, and then when pressing the button the user would find out that the pickup is actually not possible. This is not a good user experience and had to be corrected.
We had pretty much from the beginning in every account the field "Permissions to monitor this account" which was a flexible way to define who would be allowed to see the status on the resource. This list could just show the extensions or use simple patterns to define the permissions for this.
The problem is that this is a way to keep the LED completely dark or fully functions. What we needed was a mode in the middle that would just allow the on/off state. We were discussing adding another field that defines this, however it turned out that a simple extension of the pattern syntax would be easier.
What the PBX starting with version 60.3 would do is look for a flag "no" (for "no pickup") behind the pattern. This way it would be easy to mix the permissions, e.g. the pattern "44 55:np 5*" would mean that extension 44 can see anything, extension 55 would only see the on/off status while all other extensions starting with 5 would see everything. The pattern is backward compatible with previous versions, so that we don't have to worry about behavior in upgrades.