The term \gls*{declaration} is used to refer to a \gls{command} that
affects the document from that point onwards. The declaration itself
does not produce any text and, in most cases, its effect can be
localised by placing the declaration within a \gls{group}. For
example, \glsi{bfseries} is a declaration that switches the
current font weight to bold, so the following code
\begin{code}
\begin{alltt}
Here is some normal text.
\glsni{bfseries} Here is some bold text.
\end{alltt}
\end{code}%
will appear in the typeset document looking like:
\begin{resultS}[declaration.html]
Here is some normal text. \bfseries Here is some bold text.
\end{resultS}

Some declarations don't immediately have a visible effect. For
example, the declarations
\begin{definition}
\gls{raggedright}
\gls{raggedleft}
\gls{centering}
\end{definition}
only set the paragraph justification to ragged-right,
ragged-left or centred, respectively, if the
declaration is still in effect at the end of the paragraph.
That is, if it is still in effect at the next \glsni{par} or blank line.

\xminisec{Example:}
\begin{code}
This is an example paragraph illustrating the paragraph justification declarations. The default justification is fully justified.
\glsni{raggedright} The paragraph justification can be switched to
ragged-right or \glsni{raggedleft} ragged-left.
\glsni{par}
\end{code}
\begin{result}[raggedleft.html]
This is an example paragraph illustrating the paragraph justification declarations. The default justification is fully justified.
\raggedright The paragraph justification can be switched to
ragged-right or \raggedleft ragged-left.
\par
\end{result}
Above, the justification at the paragraph break is ragged-left, so
that's the justification used for the entire paragraph.
Compare with:
\begin{code}
\marg{This is an example paragraph illustrating the paragraph justification declarations. The default justification is fully
justified.
\glsni{raggedright} The paragraph justification can be switched to
ragged-right or \glsni{raggedleft} ragged-left.}
\glsni{par}
\end{code}
\begin{result}[fullyjustified.html]
\setlength{\parindent}{1.5em}% For the benefit of LaTeX2HTML
{This is an example paragraph illustrating the paragraph justification declarations. The default justification is fully justified.
\raggedright The paragraph justification can be switched to
ragged-right or \raggedleft ragged-left.}\relax
\par
\end{result}
Above, the justification at the paragraph break is fully-justified,
since both the declarations \glsni{raggedright} and
\glsni{raggedleft} are cancelled when their local scope (signified
by the curly braces) ends.
This type of mistake most often occurs when people try to centre
text doing something like:
\begin{alltt}
\marg{\glsni{centering} Some text that is supposed to
be centred.
}
\wrong
Next paragraph.
\end{alltt}
The paragraph break (blank line) must go before the closing brace.
\begin{alltt}
\marg{\glsni{centering} Some text that is supposed to
be centred.
\correct
}
Next paragraph.
\end{alltt}

\warning While we're on the subject of centred text, don't be
tempted to use \cmdname{centerline}. It's obsolete~\cite{l2tabu}.