Mysterious space before \footnote command

Question

I defined a custom name + year + title footnote format, but for some reason there is a leading space before the superscript. Where is it coming from?

The command looks like this:

\DeclareNameFormat{lastnameonly}{\namepartfamily}
\DeclareCiteCommand{\myfootcite}{}{%
    \footnote{%
        \printnames[lastnameonly]{author} (\printfield{year}), \printfield{title}
    }
}{}{}

Output:

MWE:

\documentclass{article}

\usepackage[backend=biber]{biblatex}
\bibliography{references.bib}
\begin{filecontents}{references.bib}
@article{smith01,
  author = {Smith, John},
  year = {2001},
  title = {Article title}
}
\end{filecontents}

%% Custom command giving a mysterious space
\DeclareNameFormat{lastnameonly}{\namepartfamily}
\DeclareCiteCommand{\myfootcite}{}{%
    \footnote{%
        \printnames[lastnameonly]{author} (\printfield{year}), \printfield{title}
    }
}{}{}

\begin{document}
There is a space \myfootcite{smith01}
\end{document}

Answer 1

the easy thing to do is add \unskip at the beginning of the \myfootcite definition:

%% Custom command giving a mysterious space
\DeclareNameFormat{lastnameonly}{\namepartfamily}
\DeclareCiteCommand{\myfootcite}{}{%
    \unskip
    \footnote{%
        \printnames[lastnameonly]{author} (\printfield{year}), \printfield{title}% <--
    }% <--
}{}{}

this has the effect of removing the space that immediately precedes the insertion of the command when it's applied.

the inverse of this is \ignorespaces, which will, as it says, ignore any spaces that immediately follow a command that includes it at the end.

these two commands earn their keep when careless input includes spaces at the beginning or end of some string that is to be used in a position where "clean" spacing matters, like a running head, or preceding a footnote as the example here shows.

there were also spurious spaces, removed with a % in the spots marked with <--.