add comments, metanorma/metanorma-iso#870

Author: Intelligent2013

src/main/java/org/apache/fop/fonts/GlyphMapping.java

@@ -49,7 +49,7 @@ public class GlyphMapping {
     public MinOptMax areaIPD;
     public final boolean isHyphenated;
     public final boolean isSpace;
-    public final boolean isZeroWidthSpace;
+    public final boolean isZeroWidthSpace; // to check for zero-width space (otherwise we get redundant spaces in copy-paste text from PDF)
     public boolean breakOppAfter;
     public final Font font;
     public final int level;

src/main/java/org/apache/fop/layoutmgr/inline/TextLayoutManager.java

@@ -515,6 +515,7 @@ private void addWord(int startIndex, int endIndex, int wordLength) {
         }
 
         private boolean isWordSpace(int mappingIndex) {
+            // !getGlyphMapping(mappingIndex).isZeroWidthSpace - no need add space for zero-width space, otherwise we get redundant spaces in copy-paste text from PDF
             return userAgent.isAccessibilityEnabled()
                     && mappingIndex < mappings.size() - 1 && getGlyphMapping(mappingIndex).isSpace && !getGlyphMapping(mappingIndex).isZeroWidthSpace;
         }
@@ -859,6 +860,7 @@ public List getNextKnuthElements(final LayoutContext context, final int alignmen
                 Font font = FontSelector.selectFontForCharacterInText(ch, foText, this);
                 MinOptMax ipd = MinOptMax.getInstance(font.getCharWidth(ch));
 
+                // to check for zero-width space (otherwise we get redundant spaces in copy-paste text from PDF)
                 boolean isZeroWidthSpace = (ch == CharUtilities.ZERO_WIDTH_SPACE);
 
                 mapping = new GlyphMapping(nextStart, nextStart + 1, 0, 0, ipd, false, true, isZeroWidthSpace,