Indent with tabs

There are two uses of white space in source code: indentation and alignment.

Indentation expresses the semantic level of a source line. This task falls naturally onto tabs.

• Semantically correct: one tab is one level in; a space is separation of two words, and emptiness of a character wide.
• Accessible: visually impaired people might have difficulty reading indentation too small, like 2-space; some might otherwise find indentation too large, like 8-space, too tiring to read. With tabs, they can freely adjust to their comfortable display width.
• Respectful: with tabs, users could adjust their display width to their liking; spaces force author's preference onto them.
• Less bytes: with 4-space indentation, a tab saves 3.

If you have background in Web development or other computer layout systems, think of relative and absolute sizes. A tab is like 2rem; a space is like 32px or 32pt.

Align with spaces

Tabs are not ideal for alignment: if the content before it is longer than a tab's width, the following example that looks fine with tab width 4:

routers.add({
	"/"						=> get_index,
	"/transactions/{id}"	=> get_transaction,
	"/account"				=> get_account,
})

.. looks terrible with tab width 8:

routers.add({
	"/"						=> get_index,
	"/transactions/{id}"	=> get_transaction,
	"/account"				=> get_account,
})

Here, spaces are more fit:

routers.add({
	"/"                  => get_index,
	"/transactions/{id}" => get_transaction,
	"/account"           => get_account,
})