Of course, when you have two of the same tags after each other, you can simply merge them:
b Hello World
But, if you would have two different sibling tags and would want a space between them, you could use piping to output a space between them.
For example:
b Hello
| <-- 2 spaces after the pipe
i World
Note that when specifying tag contents / piping text, the actual text content is preceded by a white space. This white space is not outputted. So, in effect, to pipe a white-space you need a |
character followed by two spaces.
If you are in an environment where trailing spaces are not preserved, you can alternatively use the following:
b Hello
=" "
i World
=
evaluates a JavaScript expression and outputs the result.
Also note that
is not the same as a space in HTML. The correct HTML entity to use is  
(or  
if you like hexadecimal numbers).
stands for non-breaking space. Its character code is 160 ( 
). The difference is that where an ordinary space is used, multiple spaces will be shown as a single space and if a line overflows, the text will continue on the next line.* Non-breaking spaces on the other hand will allways be shown. Lines will never wrap where a non-breaking space is used.
This is best illustrated with an example:
(Note the scroll bar at the bottom.)
Space ( )
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    (Note there is no scroll bar because all spaces are concatenated into one.)
* This can be overridden with the CSS white-space
property. Some elements, such as <pre>
, display all white space and line endings by default.
means you end up with two spaces in the result. – Bindweed