Dimensions can optionally be followed by limits: minimum and maximum values. For example, it is useful to specify a label size in map meters, but clamp it to a certain range of sizes, avoiding lettering that is too small to read, or so large as to be ugly and obtrusive. For example:
sets a label size to 300 map meters but clamps it to the range 8pt...24pt. It is legal to omit the third (upper) limit, as in:
Limits must not be negative. A minus sign can occur only before the main dimension; if so, the dimension, with its limits, is evaluated as if it was positive, then negated.