The file
jdk/src/java.desktop/share/classes/javax/swing/plaf/multi/doc-files/multi_tsc.html
declares a DOCTYPE of 3.2.

It should be updated to HTML 5.

One side effect that will have to be addressed at the same time is change the character encoding. It is currently written in ISO-8859-1. In general, we are using UTF-8 for our doc files. If the file is read in its current form with UTF-8, you will find the following invalid characters.

docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:273: found 1 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:275: found 1 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:281: found 1 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:311: found 1 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:334: found 3 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:335: found 3 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:336: found 7 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:339: found 7 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:340: found 9 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:341: found 9 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:342: found 7 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:343: found 7 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:344: found 7 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:345: found 3 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:349: found 3 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:350: found 7 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:353: found 3 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:360: found 1 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:362: found 1 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:373: found 1 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:376: found 1 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:395: found 1 invalid characters
docs/api/javax/swing/plaf/multi/doc-files/multi_tsc.html:477: found 1 invalid characters

 The file should be made readable with UTF-8.