poster_template: add tagged PDF (PDF/UA-2) accessibility

Enables \DocumentMetadata (pdfversion=2.0, pdfstandard=ua-2) and
tagpdf with activate-all. Adds an H1 structure tag around every
frame title via \addtobeamertemplate, wraps the overlay-only tikz
helpers (\marktopleft, \markbottomright, \credit) in artifact tags
so they don't pollute the reading order, and adds alt text to each
\includegraphics. Verified compliant with verapdf's PDF/UA-2 profile.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

poster_template/main.tex

@@ -1,7 +1,24 @@
+\DocumentMetadata{
+  pdfversion=2.0,
+  pdfstandard=ua-2,
+  lang=en-US,
+}
 \documentclass[xcolor=dvipsnames, 12pt]{beamer}
 
 \usepackage[size=custom, width=114, height=80, scale=1.5]{beamerposter}
 
+\usepackage{tagpdf}
+\tagpdfsetup{activate-all}
+
+% Tag frame titles as H1 headings for PDF accessibility
+\addtobeamertemplate{frametitle}{%
+  \tagstructbegin{tag=H1}%
+  \tagmcbegin{tag=H1}%
+}{%
+  \tagmcend%
+  \tagstructend%
+}
+
 \usepackage[absolute,overlay]{textpos}
 % set up the file to create notes in the output PDFs
 
@@ -41,10 +58,10 @@
 \tikzstyle{every picture}+=[overlay,remember picture]
 
 % add functions to circle parts of slides (e.g., in tables)
-\newcommand\marktopleft[1]{\tikz \node (marker-#1-a) at (0,1.5ex) {};}
+\newcommand\marktopleft[1]{\tagmcbegin{artifact}\tikz \node (marker-#1-a) at (0,1.5ex) {};\tagmcend}
 \newcommand\markbottomright[1]{%
-  \tikz{\node (marker-#1-b) at (0,0) {};}
-  \tikz[dashed,inner sep=3pt]{\node[violet!75,ultra thick,draw,rounded rectangle,fit=(marker-#1-a.center) (marker-#1-b.center)] {};}}
+  \tagmcbegin{artifact}\tikz{\node (marker-#1-b) at (0,0) {};}\tagmcend
+  \tagmcbegin{artifact}\tikz[dashed,inner sep=3pt]{\node[violet!75,ultra thick,draw,rounded rectangle,fit=(marker-#1-a.center) (marker-#1-b.center)] {};}\tagmcend}
 
 % DEPRECATED function to build a huge centered dropshadow
 \newcommand\dropshadow[3]{%
@@ -149,7 +166,9 @@
 %\useoutertheme{infolines}p
 %\usepackage[breaklinks]{hyperref}
 
-\hypersetup{colorlinks=true, linkcolor=Black, citecolor=Black, filecolor=makopurple1, urlcolor=Plum, unicode=true}
+\hypersetup{colorlinks=true, linkcolor=Black, citecolor=Black, filecolor=makopurple1, urlcolor=Plum, unicode=true,
+    pdflang={en-US},
+    pdfdisplaydoctitle=true}
 
 % create a boldface version of the header
 \setbeamerfont{frametitle}{series=\bfseries}
@@ -185,7 +204,7 @@
 \newcommand{\credit}[1]{%
   \tikz[overlay]{\node at (current page.south east)
     [anchor=south east,yshift=1.3em,xshift=0.35em]
-    {\smaller {[}#1{]}};}}
+    {\tagmcbegin{artifact}\smaller {[}#1{]}\tagmcend};}}
 \begin{document}
 
 \begin{frame}[t]{}
@@ -195,7 +214,7 @@
     
     \vspace*{1ex}
     
-    \includegraphics[width=8cm]{figures/uw_logo}
+    \includegraphics[width=8cm,alt={University of Washington logo}]{figures/uw_logo}
     \vspace*{1ex}
   \end{textblock}
 
@@ -248,7 +267,7 @@
   \end{textblock}
 
   \begin{textblock}{2}(122,0)
-    \includegraphics[width=6.5cm]{figures/logo}
+    \includegraphics[width=6.5cm,alt={Community Data Science Collective logo}]{figures/logo}
     
     \vspace*{1ex}
   \end{textblock}
@@ -279,7 +298,7 @@
 \vspace{1em}
 \begin{figure}
 \centering
-\includegraphics[width=0.8\textwidth]{figures/taboo topics hypotheses.jpg}
+\includegraphics[width=0.8\textwidth,alt={Diagram of project hypotheses}]{figures/taboo topics hypotheses.jpg}
 \end{figure}  
 
 
@@ -301,7 +320,7 @@ With billions of viewers, Wikipedia is one of the top ten most visited sites on
 \vspace{0.3em}
 \begin{center}
 \begin{figure}
-\includegraphics[width=0.8\textwidth]{figures/viewsBox.pdf}
+\includegraphics[width=0.8\textwidth,alt={Boxplot of article ranks by popularity}]{figures/viewsBox.pdf}
 \caption{Rank of articles in our sample versus all articles with dictionary salience. The most popular article is ranked ``1''.} 
 \end{figure}
 \end{center}
@@ -323,7 +342,7 @@ Definitions tagged with euphemistic usages were marked as taboo. We extracted al
 
 \begin{figure}
 \centering 
-\includegraphics[width=\textwidth]{figures/member.png}
+\includegraphics[width=\textwidth,alt={Screenshot of the Wiktionary definition of ``member''}]{figures/member.png}
 
 \caption{The Wiktionary definition of ``member''---which has meanings ranging from the organizational to the anatomical.}
     \label{fig:wiktEntry}
@@ -340,7 +359,7 @@ To develop a comparison sample, we filtered the population of articles to just t
 
 \begin{figure}
     \centering
-    \includegraphics[width=.9\textwidth]{figures/V2 Taboo Topics Analytical Pipeline.pdf}
+    \includegraphics[width=.9\textwidth,alt={Flowchart of the analytical pipeline}]{figures/V2 Taboo Topics Analytical Pipeline.pdf}
     \caption{Our analytical pipeline first extracts n-grams, labeling them taboo if they are drawn from definitions tagged as euphemistic. Our samples are drawn from those articles that match these n-grams.} \label{fig:pipeline}
 \end{figure}
 \end{block}
@@ -352,7 +371,7 @@ To develop a comparison sample, we filtered the population of articles to just t
 \vspace{0.3em}
 \begin{figure}
 \centering
-\includegraphics[width=0.5\textwidth]{figures/volumeBox.pdf}
+\includegraphics[width=0.5\textwidth,alt={Boxplot of contribution volume}]{figures/volumeBox.pdf}
 \caption{Taboo articles receive more contributions than comparable articles.}
 \label{fig:volumeBox}
 \end{figure}  
@@ -367,7 +386,7 @@ To develop a comparison sample, we filtered the population of articles to just t
 \vspace{0.3em}
 \begin{figure}
 \centering
-\includegraphics[width=0.5\textwidth]{figures/boxQualitySrc.pdf}
+\includegraphics[width=0.5\textwidth,alt={Boxplot of article quality}]{figures/boxQualitySrc.pdf}
 \caption{Articles about taboo subjects exceed the quality of our comparison set.}
 \label{fig:ageGrowth}
 \end{figure}  
@@ -382,7 +401,7 @@ To develop a comparison sample, we filtered the population of articles to just t
 \vspace{0.3em}
 \begin{center}
 \begin{figure}
-\includegraphics[width=0.5\textwidth]{figures/damageRate.pdf}
+\includegraphics[width=0.5\textwidth,alt={Plot of damage rates by article category}]{figures/damageRate.pdf}
 \caption{The rate of damaging contributions to taboo subjects is higher.} 
 \end{figure}
 \end{center}
@@ -396,12 +415,12 @@ Editors of taboo subjects are less likely to use an account, have less experienc
 
 \begin{figure}
 %\begin{minipage}{0.45\textwidth}
-\includegraphics[width=.45\textwidth]{figures/mailProp.pdf}
+\includegraphics[width=.45\textwidth,alt={Proportion of contributors who disclose an email address}]{figures/mailProp.pdf}
 \end{figure}
 %\end{minipage}\hfill
 %\begin{minipage}{0.45\textwidth}
 \begin{figure}
-\includegraphics[width=.45\textwidth]{figures/genderProp.pdf}
+\includegraphics[width=.45\textwidth,alt={Proportion of contributors who disclose gender}]{figures/genderProp.pdf}
 %\end{minipage}\hfill
 \end{figure}