As with all web content (not just TiddlyWiki), HTML content is rendered "inline", which joins separate lines and reduces multiple spaces to single spaces.
Thus, the following:
foo bar
baz mumble frotz
gronk
snork snerfle argle bargle
is displayed as:
foo bar baz mumble frotz gronk snork snerfle argle bargle
To force a newline within HTML content, it is standard practice to embed <br/> where you want the newline to occur.
Of course, this can be somewhat inconvenient when you have multiple lines of content for which you want each line to remain separate.
In this case, you can use CSS to control the "white-space" handling, like this:
<blockquote style="white-space:pre;">
line one
line two
line three
</blockquote>
You can also accomplish this using a CSS *classname*:
<style> .whitespace { white-space:pre; } </style>
<blockquote class="whitespace">
line one
line two
line three
</blockquote>
The same CSS class technique can also be applied to TW wikitext blockquotes, like this:
<style> .whitespace { white-space:pre; } </style>
<<<.whitespace
line1
line2
line3
<<<
Note that, rather than putting the <style>...</style> directly in the tiddler content, it is better to put it in a separate tiddler which will define the class once for use as many times as you like:
1) create a tiddler, e.g., MyStyles, tagged with $:/tags/Stylesheet, containing:
.whitespace { white-space:pre; }
2) Use that CSS class anywhere you like:
<<<.whitespace
line 1
line 2
line 3
<<<
enjoy,
-e