Due to my personal experience it looks like that value for vertexweights isn't limited. Even negative values are valid.
There is no absolute value, one vertex will be affected relative to the value of each related bone.
The absolute weight(Range 0 to 1) gets calculated this way:
Weight / SumOfAllRelatedWeights
For example:
1. If there is only one bone, each vertex with weight > 0 will be affected by 100 %
2. Two bones containing the same weight (like 1, 0.32, 530.2 or whatever) will affect 50% each.
3. Two bones, first contains value 128, second 256:
First bone affects vertex by 33%, second one by 66%.
There is no absolute value, one vertex will be affected relative to the value of each related bone.
The absolute weight(Range 0 to 1) gets calculated this way:
Weight / SumOfAllRelatedWeights
For example:
1. If there is only one bone, each vertex with weight > 0 will be affected by 100 %
2. Two bones containing the same weight (like 1, 0.32, 530.2 or whatever) will affect 50% each.
3. Two bones, first contains value 128, second 256:
First bone affects vertex by 33%, second one by 66%.