我知道，我可以用类似 来定义一些unicode字符\DeclareUnicodeCharacter{3B5}{$\epsilon$}。但是，对于一些已经由LaTeX引擎支持的字符，似乎不一定这样做，例如下面示例第一行中列出的字符。
\documentclass{article}
\usepackage[utf8]{inputenc}
\begin{document}
List of some supported unicode characters:
é è ä ¿ … ß œ
List of some non-supported unicode characters%
\footnote{See source, they are not displayed of course!}:
% ε Ω ± −
\end{document}
那么，是否可以列出 LaTeX 引擎支持的所有 unicode 字符？
答案1
正如 Ulrike 所评论的那样，列表是开放的，如果您使用fontenc加载特定字体编码，则如果存在匹配的文件，则会进行匹配的 Unicode 输入声明.dfu。此外，针对 CJK 脚本或阿拉伯语的特定包可能会定义大范围，但是默认情况下，格式本身的定义涵盖 T1 和 OT1 以及一些 OMS 编码。
如果您查看utf8enc.dfu基础 latex 目录中的 for 文件，它（当前）具有以下定义，则 tha 显示核心格式已知的定义，但在格式创建期间仅加载子集 t1enc.dfu、ot1enc.dfu 和 omsenc.dfu。
在评论中您提到 U+00B5（micro），它不受默认字体集支持（因此不受默认 inputenc 映射支持），但如果您通过包加载 TS1 编码textcomp，\textmu则会被定义并ts1enc.dfu加载：
\documentclass{article}
\usepackage{textcomp}
\begin{document}
[µ]
\end{document}
注意上述文件的日志将显示
/usr/local/texlive/2019/texmf-dist/tex/latex/base/ts1enc.dfu
制作格式时输入的文件有：
ot1enc.dfu
\DeclareUnicodeCharacter{00A0}{\nobreakspace}
\DeclareUnicodeCharacter{00A1}{\textexclamdown}
\DeclareUnicodeCharacter{00A3}{\textsterling}
\DeclareUnicodeCharacter{00AD}{\-}
\DeclareUnicodeCharacter{00B8}{\c\ }
\DeclareUnicodeCharacter{00BF}{\textquestiondown}
\DeclareUnicodeCharacter{00C5}{\r A}
\DeclareUnicodeCharacter{00C6}{\AE}
\DeclareUnicodeCharacter{00D8}{\O}
\DeclareUnicodeCharacter{00DF}{\ss}
\DeclareUnicodeCharacter{00E6}{\ae}
\DeclareUnicodeCharacter{00EC}{\@tabacckludge`\i}
\DeclareUnicodeCharacter{00ED}{\@tabacckludge'\i}
\DeclareUnicodeCharacter{00EE}{\^\i}
\DeclareUnicodeCharacter{00EF}{\"\i}
\DeclareUnicodeCharacter{00F8}{\o}
\DeclareUnicodeCharacter{0131}{\i}
\DeclareUnicodeCharacter{0141}{\L}
\DeclareUnicodeCharacter{0142}{\l}
\DeclareUnicodeCharacter{0152}{\OE}
\DeclareUnicodeCharacter{0153}{\oe}
\DeclareUnicodeCharacter{0174}{\^W}
\DeclareUnicodeCharacter{0175}{\^w}
\DeclareUnicodeCharacter{0176}{\^Y}
\DeclareUnicodeCharacter{0177}{\^y}
\DeclareUnicodeCharacter{0218}{\textcommabelow S}
\DeclareUnicodeCharacter{0219}{\textcommabelow s}
\DeclareUnicodeCharacter{021A}{\textcommabelow T}
\DeclareUnicodeCharacter{021B}{\textcommabelow t}
\DeclareUnicodeCharacter{0237}{\j}
\DeclareUnicodeCharacter{2013}{\textendash}
\DeclareUnicodeCharacter{2014}{\textemdash}
\DeclareUnicodeCharacter{2018}{\textquoteleft}
\DeclareUnicodeCharacter{2019}{\textquoteright}
\DeclareUnicodeCharacter{201C}{\textquotedblleft}
\DeclareUnicodeCharacter{201D}{\textquotedblright}
t1enc.dfu
\DeclareUnicodeCharacter{00A0}{\nobreakspace}
\DeclareUnicodeCharacter{00A1}{\textexclamdown}
\DeclareUnicodeCharacter{00A3}{\textsterling}
\DeclareUnicodeCharacter{00AB}{\guillemotleft}
\DeclareUnicodeCharacter{00AD}{\-}
\DeclareUnicodeCharacter{00BB}{\guillemotright}
\DeclareUnicodeCharacter{00BF}{\textquestiondown}
\DeclareUnicodeCharacter{00C0}{\@tabacckludge`A}
\DeclareUnicodeCharacter{00C1}{\@tabacckludge'A}
\DeclareUnicodeCharacter{00C2}{\^A}
\DeclareUnicodeCharacter{00C3}{\~A}
\DeclareUnicodeCharacter{00C4}{\"A}
\DeclareUnicodeCharacter{00C5}{\r A}
\DeclareUnicodeCharacter{00C6}{\AE}
\DeclareUnicodeCharacter{00C7}{\c C}
\DeclareUnicodeCharacter{00C8}{\@tabacckludge`E}
\DeclareUnicodeCharacter{00C9}{\@tabacckludge'E}
\DeclareUnicodeCharacter{00CA}{\^E}
\DeclareUnicodeCharacter{00CB}{\"E}
\DeclareUnicodeCharacter{00CC}{\@tabacckludge`I}
\DeclareUnicodeCharacter{00CD}{\@tabacckludge'I}
\DeclareUnicodeCharacter{00CE}{\^I}
\DeclareUnicodeCharacter{00CF}{\"I}
\DeclareUnicodeCharacter{00D0}{\DH}
\DeclareUnicodeCharacter{00D1}{\~N}
\DeclareUnicodeCharacter{00D2}{\@tabacckludge`O}
\DeclareUnicodeCharacter{00D3}{\@tabacckludge'O}
\DeclareUnicodeCharacter{00D4}{\^O}
\DeclareUnicodeCharacter{00D5}{\~O}
\DeclareUnicodeCharacter{00D6}{\"O}
\DeclareUnicodeCharacter{00D8}{\O}
\DeclareUnicodeCharacter{00D9}{\@tabacckludge`U}
\DeclareUnicodeCharacter{00DA}{\@tabacckludge'U}
\DeclareUnicodeCharacter{00DB}{\^U}
\DeclareUnicodeCharacter{00DC}{\"U}
\DeclareUnicodeCharacter{00DD}{\@tabacckludge'Y}
\DeclareUnicodeCharacter{00DE}{\TH}
\DeclareUnicodeCharacter{00DF}{\ss}
\DeclareUnicodeCharacter{00E0}{\@tabacckludge`a}
\DeclareUnicodeCharacter{00E1}{\@tabacckludge'a}
\DeclareUnicodeCharacter{00E2}{\^a}
\DeclareUnicodeCharacter{00E3}{\~a}
\DeclareUnicodeCharacter{00E4}{\"a}
\DeclareUnicodeCharacter{00E5}{\r a}
\DeclareUnicodeCharacter{00E6}{\ae}
\DeclareUnicodeCharacter{00E7}{\c c}
\DeclareUnicodeCharacter{00E8}{\@tabacckludge`e}
\DeclareUnicodeCharacter{00E9}{\@tabacckludge'e}
\DeclareUnicodeCharacter{00EA}{\^e}
\DeclareUnicodeCharacter{00EB}{\"e}
\DeclareUnicodeCharacter{00EC}{\@tabacckludge`\i}
\DeclareUnicodeCharacter{00ED}{\@tabacckludge'\i}
\DeclareUnicodeCharacter{00EE}{\^\i}
\DeclareUnicodeCharacter{00EF}{\"\i}
\DeclareUnicodeCharacter{00F0}{\dh}
\DeclareUnicodeCharacter{00F1}{\~n}
\DeclareUnicodeCharacter{00F2}{\@tabacckludge`o}
\DeclareUnicodeCharacter{00F3}{\@tabacckludge'o}
\DeclareUnicodeCharacter{00F4}{\^o}
\DeclareUnicodeCharacter{00F5}{\~o}
\DeclareUnicodeCharacter{00F6}{\"o}
\DeclareUnicodeCharacter{00F8}{\o}
\DeclareUnicodeCharacter{00F9}{\@tabacckludge`u}
\DeclareUnicodeCharacter{00FA}{\@tabacckludge'u}
\DeclareUnicodeCharacter{00FB}{\^u}
\DeclareUnicodeCharacter{00FC}{\"u}
\DeclareUnicodeCharacter{00FD}{\@tabacckludge'y}
\DeclareUnicodeCharacter{00FE}{\th}
\DeclareUnicodeCharacter{00FF}{\"y}
\DeclareUnicodeCharacter{0100}{\@tabacckludge=A}
\DeclareUnicodeCharacter{0101}{\@tabacckludge=a}
\DeclareUnicodeCharacter{0102}{\u A}
\DeclareUnicodeCharacter{0103}{\u a}
\DeclareUnicodeCharacter{0104}{\k A}
\DeclareUnicodeCharacter{0105}{\k a}
\DeclareUnicodeCharacter{0106}{\@tabacckludge'C}
\DeclareUnicodeCharacter{0107}{\@tabacckludge'c}
\DeclareUnicodeCharacter{0108}{\^C}
\DeclareUnicodeCharacter{0109}{\^c}
\DeclareUnicodeCharacter{010A}{\.C}
\DeclareUnicodeCharacter{010B}{\.c}
\DeclareUnicodeCharacter{010C}{\v C}
\DeclareUnicodeCharacter{010D}{\v c}
\DeclareUnicodeCharacter{010E}{\v D}
\DeclareUnicodeCharacter{010F}{\v d}
\DeclareUnicodeCharacter{0110}{\DJ}
\DeclareUnicodeCharacter{0111}{\dj}
\DeclareUnicodeCharacter{0112}{\@tabacckludge=E}
\DeclareUnicodeCharacter{0113}{\@tabacckludge=e}
\DeclareUnicodeCharacter{0114}{\u E}
\DeclareUnicodeCharacter{0115}{\u e}
\DeclareUnicodeCharacter{0116}{\.E}
\DeclareUnicodeCharacter{0117}{\.e}
\DeclareUnicodeCharacter{0118}{\k E}
\DeclareUnicodeCharacter{0119}{\k e}
\DeclareUnicodeCharacter{011A}{\v E}
\DeclareUnicodeCharacter{011B}{\v e}
\DeclareUnicodeCharacter{011C}{\^G}
\DeclareUnicodeCharacter{011D}{\^g}
\DeclareUnicodeCharacter{011E}{\u G}
\DeclareUnicodeCharacter{011F}{\u g}
\DeclareUnicodeCharacter{0120}{\.G}
\DeclareUnicodeCharacter{0121}{\.g}
\DeclareUnicodeCharacter{0122}{\c G}
\DeclareUnicodeCharacter{0123}{\c g}
\DeclareUnicodeCharacter{0124}{\^H}
\DeclareUnicodeCharacter{0125}{\^h}
\DeclareUnicodeCharacter{0128}{\~I}
\DeclareUnicodeCharacter{0129}{\~\i}
\DeclareUnicodeCharacter{012A}{\@tabacckludge=I}
\DeclareUnicodeCharacter{012B}{\@tabacckludge=\i}
\DeclareUnicodeCharacter{012C}{\u I}
\DeclareUnicodeCharacter{012D}{\u\i}
\DeclareUnicodeCharacter{012E}{\k I}
\DeclareUnicodeCharacter{012F}{\k\i}
\DeclareUnicodeCharacter{0130}{\.I}
\DeclareUnicodeCharacter{0131}{\i}
\DeclareUnicodeCharacter{0132}{\IJ}
\DeclareUnicodeCharacter{0133}{\ij}
\DeclareUnicodeCharacter{0134}{\^J}
\DeclareUnicodeCharacter{0135}{\^\j}
\DeclareUnicodeCharacter{0136}{\c K}
\DeclareUnicodeCharacter{0137}{\c k}
\DeclareUnicodeCharacter{0139}{\@tabacckludge'L}
\DeclareUnicodeCharacter{013A}{\@tabacckludge'l}
\DeclareUnicodeCharacter{013B}{\c L}
\DeclareUnicodeCharacter{013C}{\c l}
\DeclareUnicodeCharacter{013D}{\v L}
\DeclareUnicodeCharacter{013E}{\v l}
\DeclareUnicodeCharacter{0141}{\L}
\DeclareUnicodeCharacter{0142}{\l}
\DeclareUnicodeCharacter{0143}{\@tabacckludge'N}
\DeclareUnicodeCharacter{0144}{\@tabacckludge'n}
\DeclareUnicodeCharacter{0145}{\c N}
\DeclareUnicodeCharacter{0146}{\c n}
\DeclareUnicodeCharacter{0147}{\v N}
\DeclareUnicodeCharacter{0148}{\v n}
\DeclareUnicodeCharacter{014A}{\NG}
\DeclareUnicodeCharacter{014B}{\ng}
\DeclareUnicodeCharacter{014C}{\@tabacckludge=O}
\DeclareUnicodeCharacter{014D}{\@tabacckludge=o}
\DeclareUnicodeCharacter{014E}{\u O}
\DeclareUnicodeCharacter{014F}{\u o}
\DeclareUnicodeCharacter{0150}{\H O}
\DeclareUnicodeCharacter{0151}{\H o}
\DeclareUnicodeCharacter{0152}{\OE}
\DeclareUnicodeCharacter{0153}{\oe}
\DeclareUnicodeCharacter{0154}{\@tabacckludge'R}
\DeclareUnicodeCharacter{0155}{\@tabacckludge'r}
\DeclareUnicodeCharacter{0156}{\c R}
\DeclareUnicodeCharacter{0157}{\c r}
\DeclareUnicodeCharacter{0158}{\v R}
\DeclareUnicodeCharacter{0159}{\v r}
\DeclareUnicodeCharacter{015A}{\@tabacckludge'S}
\DeclareUnicodeCharacter{015B}{\@tabacckludge's}
\DeclareUnicodeCharacter{015C}{\^S}
\DeclareUnicodeCharacter{015D}{\^s}
\DeclareUnicodeCharacter{015E}{\c S}
\DeclareUnicodeCharacter{015F}{\c s}
\DeclareUnicodeCharacter{0160}{\v S}
\DeclareUnicodeCharacter{0161}{\v s}
\DeclareUnicodeCharacter{0162}{\c T}
\DeclareUnicodeCharacter{0163}{\c t}
\DeclareUnicodeCharacter{0164}{\v T}
\DeclareUnicodeCharacter{0165}{\v t}
\DeclareUnicodeCharacter{0168}{\~U}
\DeclareUnicodeCharacter{0169}{\~u}
\DeclareUnicodeCharacter{016A}{\@tabacckludge=U}
\DeclareUnicodeCharacter{016B}{\@tabacckludge=u}
\DeclareUnicodeCharacter{016C}{\u U}
\DeclareUnicodeCharacter{016D}{\u u}
\DeclareUnicodeCharacter{016E}{\r U}
\DeclareUnicodeCharacter{016F}{\r u}
\DeclareUnicodeCharacter{0170}{\H U}
\DeclareUnicodeCharacter{0171}{\H u}
\DeclareUnicodeCharacter{0172}{\k U}
\DeclareUnicodeCharacter{0173}{\k u}
\DeclareUnicodeCharacter{0174}{\^W}
\DeclareUnicodeCharacter{0175}{\^w}
\DeclareUnicodeCharacter{0176}{\^Y}
\DeclareUnicodeCharacter{0177}{\^y}
\DeclareUnicodeCharacter{0178}{\"Y}
\DeclareUnicodeCharacter{0179}{\@tabacckludge'Z}
\DeclareUnicodeCharacter{017A}{\@tabacckludge'z}
\DeclareUnicodeCharacter{017B}{\.Z}
\DeclareUnicodeCharacter{017C}{\.z}
\DeclareUnicodeCharacter{017D}{\v Z}
\DeclareUnicodeCharacter{017E}{\v z}
\DeclareUnicodeCharacter{01CD}{\v A}
\DeclareUnicodeCharacter{01CE}{\v a}
\DeclareUnicodeCharacter{01CF}{\v I}
\DeclareUnicodeCharacter{01D0}{\v \i}
\DeclareUnicodeCharacter{01D1}{\v O}
\DeclareUnicodeCharacter{01D2}{\v o}
\DeclareUnicodeCharacter{01D3}{\v U}
\DeclareUnicodeCharacter{01D4}{\v u}
\DeclareUnicodeCharacter{01E2}{\@tabacckludge=\AE}
\DeclareUnicodeCharacter{01E3}{\@tabacckludge=\ae}
\DeclareUnicodeCharacter{01E6}{\v G}
\DeclareUnicodeCharacter{01E7}{\v g}
\DeclareUnicodeCharacter{01E8}{\v K}
\DeclareUnicodeCharacter{01E9}{\v k}
\DeclareUnicodeCharacter{01EA}{\k O}
\DeclareUnicodeCharacter{01EB}{\k o}
\DeclareUnicodeCharacter{01F0}{\v\j}
\DeclareUnicodeCharacter{01F4}{\@tabacckludge'G}
\DeclareUnicodeCharacter{01F5}{\@tabacckludge'g}
\DeclareUnicodeCharacter{0218}{\textcommabelow S}
\DeclareUnicodeCharacter{0219}{\textcommabelow s}
\DeclareUnicodeCharacter{021A}{\textcommabelow T}
\DeclareUnicodeCharacter{021B}{\textcommabelow t}
\DeclareUnicodeCharacter{0232}{\@tabacckludge=Y}
\DeclareUnicodeCharacter{0233}{\@tabacckludge=y}
\DeclareUnicodeCharacter{0237}{\j}
\DeclareUnicodeCharacter{02D9}{\.{}}
\DeclareUnicodeCharacter{02DB}{\k{}}
\DeclareUnicodeCharacter{1E02}{\.B}
\DeclareUnicodeCharacter{1E03}{\.b}
\DeclareUnicodeCharacter{1E9E}{\SS}
\DeclareUnicodeCharacter{200C}{\textcompwordmark}
\DeclareUnicodeCharacter{2010}{-}
\DeclareUnicodeCharacter{2011}{\mbox{-}}
\DeclareUnicodeCharacter{2012}{\textendash}
\DeclareUnicodeCharacter{2013}{\textendash}
\DeclareUnicodeCharacter{2014}{\textemdash}
\DeclareUnicodeCharacter{2015}{\textemdash}
\DeclareUnicodeCharacter{2018}{\textquoteleft}
\DeclareUnicodeCharacter{2019}{\textquoteright}
\DeclareUnicodeCharacter{201A}{\quotesinglbase}
\DeclareUnicodeCharacter{201C}{\textquotedblleft}
\DeclareUnicodeCharacter{201D}{\textquotedblright}
\DeclareUnicodeCharacter{201E}{\quotedblbase}
\DeclareUnicodeCharacter{2030}{\textperthousand}
\DeclareUnicodeCharacter{2031}{\textpertenthousand}
\DeclareUnicodeCharacter{2039}{\guilsinglleft}
\DeclareUnicodeCharacter{203A}{\guilsinglright}
\DeclareUnicodeCharacter{2423}{\textvisiblespace}
\DeclareUnicodeCharacter{1E20}{\@tabacckludge=G}
\DeclareUnicodeCharacter{1E21}{\@tabacckludge=g}
omsenc.dfu
\DeclareUnicodeCharacter{00A7}{\textsection}
\DeclareUnicodeCharacter{00B6}{\textparagraph}
\DeclareUnicodeCharacter{00B7}{\textperiodcentered}
\DeclareUnicodeCharacter{2020}{\textdagger}
\DeclareUnicodeCharacter{2021}{\textdaggerdbl}
\DeclareUnicodeCharacter{2022}{\textbullet}
utf8enc.dfu包括基本格式的所有定义（但由于空间不足，无法在此列出）