When using Ruby on Rails, ERb (embedded Ruby) is used a LOT in the X/HTML. There are two types of ERb,
An evaluation block:
<% some_code %>
And an output block:
<%= @print_this_variable %>
These blocks are necessary when using Rails, and I've noticed that when I do a 'View Source' (via the Web Developer addon for Firefox, of course), I see a lot of funky spacing and line breaking where the ERb's have been evaluated. Probably fine for most people, but it makes reading the outputted HTML code a hassle.
It turns out that there are really three ways to use the evaluation ERb that can affect your spacing and line-breaking.
Firstly, the output block is used just like you'd expect to use it. If your code says this:
<p>
Text before ERb.
<%= "code_goes_here" %>
Text after ERb
</p>
The resulting HTML will look just like this:
<p>
Text before ERb.
code_goes_here
Text after ERb
</p>
Evaluation block use #1: If you just put a block, it will cause a line break after the block in the HTML, so if you had this in your code:
<p>
Text before ERb.
<% some_code %>
Text after ERb
</p>
The resulting HTML code would look like this:
<p>
Text before ERb.
Text after ERb
</p>
Evaluation block use #2: If you add a dash(-) at the end of the block, it will prevent it from adding a line break. So, if your code looks like this:
<p>
Text before ERb.
<% some_code -%>
Text after ERb
</p>
The resulting HTML code would look like this:
<p>
Text before ERb.
Text after ERb
</p>
The line break is gone, but the space taken by the block is still there. That leads us to. . .
Evaluation block use #3: If you add a dash(-) at the beginning AND end of the block, it will prevent it from adding a line break AND remove the leading space it would have taken up. So, if your code looks like this:
<p>
Text before ERb.
<%- some_code -%>
Text after ERb
</p>
The resulting HTML code would look like this:
<p>
Text before ERb.
Text after ERb
</p>
You'd never know there was a code block there! Is this useful? I don't know... maybe.
