# Token not allowed (hyperref) .. removing \<def>-command'

I am getting a curious warning after recompiling a tex file with pdflatex. I don't think I got the same warning in the past, and am not aware of any changes to the document. I am getting the same error on my local installation and also on overleaf.

LaTeX Font Info:    Font shape OMS/cmr/m/n' in size <10> not available
(Font)              Font shape OMS/cmsy/m/n' tried instead on input
line 84.

Overfull \hbox (2.22221pt too wide) has occurred while \output is active
[]
[]

Package hyperref Warning: Token not allowed in a PDF string
(PDFDocEncoding):
(hyperref)                removing \<def>-command' on input line 87.


Line 87, is just an \item in an itemized. If I comment it out, I get the warning in the next line. If I comment the whole block of itemized, I get the warning later.

The preambel looks like this:

\documentclass[review]{elsarticle}

\usepackage{lineno}
\usepackage[english]{babel}


Any ideas?

Thank you for your replies. The word "macro" was key. Unfortunately, this is probably a very idiosyncratic problem. However, it may still be useful for others. Here, it arose from our desire to have two corresponding authors on the manuscript. We are using an Elsevier template, which didn't allow for that, so I wrote our own macro, like so:

\author[address]{My Name\corref{thecorrespondingauthors}}

\cortext[thecorrespondingauthors]{Corresponding authors: email1@uni.edu (me), email2@uni.edu (other)}


However, the \corref has to be outside the brackets around the author names, like so:

\author[address]{My Name}\corref{thecorrespondingauthors}

Macros cannot be defined, when text is put into PDF bookmarks or information entries. Also, PDF viewers do not about TeX. Therefore, hyperref tries to filter out at least some of the stuff that is not text.
Try to make a minimal working example (MWE), if you are interested, what caused the warning in more detail. A starting point is the line number in the warning message. Maybe, line 87 contains a \section or similar command, whose title contains a definition of some kind.
Sometimes, the titles of \section, \paragraph and friends are executed at the start of the next paragraph. Thus, if \item starts a new paragraph on line 87, then the section command is before that line.
As workaround, package hyperref provides the macro \texorpdfstring{<TeX stuff>}{<replacement for bookmarks>} to replace TeX stuff that is not allowed in bookmarks by harmless text.