Why can't a numeric range involving non-single-digit numbers be expressed in a regex character class?
Why is the regex to match numbers from 1 to 10 commonly written as follows?
[1-9]|10
Instead of:
[1-10]
Or this:
[1-(10)]
Solution
Sometime a good drawing worth 1000 words...
Here are the three propositions in your question and the way a regex flavour would understand them:
[1-9]|10
[1-10]
[1-(10)]
Invalid regexp !!
This regex is invalid because a range is opened (1-) with a digit but not closed with another digit (ends with ().
A range is usually bound with digits on both sides or letters on both sides.
Images generated with Debuggex
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