organic chemistry - IUPAC naming - choosing the main branch

What are the rules for choosing main branch?

Wikipedia states:

Identification of the parent hydrocarbon chain. This chain must obey the following rules, in order of precedence:

1. It should have the maximum number of substituents of the suffix functional group. By suffix, it is meant that the parent functional group should have a suffix, unlike halogen substituents. If more than one functional group is present, the one with highest precedence should be used.


2. It should have the maximum number of multiple bonds


3. It should have the maximum number of single bonds.


4. It should have the maximum length.

I don't understand how 3 and 4 differ. Which single bonds are we counting? Only carbon-carbon single bonds in the main chain, right?

Also, I heard there is a rule that says if you've two equal length chains, then choose the more substituted one. Why is it not given here?

And now now imagine you've two choices for a chain, like this:

The chemdoodle program gives the name as 2-(1-Hydroxybutyl)-3-methylhexanoic acid .

I simply do not understand why the methyl substituted chain is chosen instead of hydroxy substituted one and how that fits with IUPAC rules given in Wikipedia.