css - What does hash (#) sign do outside loops in SASS? -

i've come across use of hash sign outside of loop in sass , i'm not sure it's used or reason is.

what's difference between these 2 examples please? both output same css first doesn't allow classes elements. why first example in use in places?

#{h1, h2, h3, h4, h5} {   color: #000; }  h1, h2, h3, h4, h5 {   color: #000; }

there 1 exception this, though: when using #{} interpolation, quoted strings unquoted. makes easier use e.g. selector names in mixins. example.

so technique used allow using sass values in selectors. e.g.:

$gutter: 10;  .grid#{$gutter} {     background: red; }

now question. don't see reason why use string interpolation in selector:

#{h1, h2, h3, h4, h5} {     color: #000; }

my best guess sass variable added later selector, or selector replaced variable.

Macro