Is Process Priority has Defined classes..?

Is Process Priority has Defined classes..?

I am searching for an document or related to Processes Priority levels.
In Linux related documentation does not talk about priority levels or Priority classes. It only provide range of nice values.
User can set any value within that range. Kernel provides min and max limits for priority.
Currently “GNOME System Monitor” shows Process Priority names like “ Very High , High , Normal , Low , Very low ” and each one has own nice value range. Related to these names i didn't got any documents as such.
In 2004, A bug was raised in “GNOME.org” against “GNOME System Monitor” Bug 131802.
The bug describes that “GNOME System Monitor” should not make references to "nice." nice has confusing semantics, mostly due to lower values being higher priority.
In 2011, A The patch adds a priority column in the process table to show the nice value in a human-understandable way, and show it by default.
I refered the https://bug131802.bugzilla-attachments.gnome.org/attachment.cgi?id=202180
And referd function “get_nice_level()” in the source code for “gnome-system-monitor”.
Below is the function template from the same file.
static gchar * get_nice_level (gint nice) { if (nice < -7) return _("(Very High Priority)"); else if (nice < -2) return _("(High Priority)"); else if (nice < 3) return _("(Normal Priority)"); else if (nice < 7) return _("(Low Priority)"); else return _("(Very Low Priority)"); }
These are my questions:
The values defined by / for GNOME System Monitor, they are that tool specific ?
Is Gnome System Monitor is actually putting a process to that priority ? Is Kernel also treat that process in that priority which is changed in Gnome System Monitor?
Is there any where i can find that these are the newly defined priority classes for different priority levels? Is this classes used across all the Distributions.?
Thanks. Shri Hari.