Add substitute_with_block method to TextRun, that can take a block wtih access to MatchData with regex capture groups etc

README.md

@@ -130,6 +130,14 @@ doc.paragraphs.each do |p|
   end
 end
 
+# Substitute text with access to captures, note block arg is a MatchData, a bit
+# different than String.gsub. https://ruby-doc.org/3.3.7/MatchData.html
+doc.paragraphs.each do |p|
+  p.each_text_run do |tr|
+    tr.substitute_with_block(/total: (\d+)/) { |match_data| "total: #{match_data[1].to_i * 10}" }
+  end
+end
+
 # Save document to specified path
 doc.save('example-edited.docx')
 ```
@@ -145,7 +153,7 @@ doc = Docx::Document.open('tables.docx')
 # Iterate over each table
 doc.tables.each do |table|
   last_row = table.rows.last
-  
+
   # Copy last row and insert a new one before last row
   new_row = last_row.copy
   new_row.insert_before(last_row)

lib/docx/containers/text_run.rb

@@ -57,6 +57,19 @@ def substitute(match, replacement)
           reset_text
         end
 
+        # Weird things with how $1/$2 in regex blocks are handled means we can't just delegate
+        # block to gsub to get block, we have to do it this way, with a block that gets a MatchData,
+        # from which captures and other match data can be retrieved.
+        # https://ruby-doc.org/3.3.7/MatchData.html
+        def substitute_with_block(match, &block)
+          @text_nodes.each do |text_node|
+            text_node.content = text_node.content.gsub(match) { |_unused_matched_string|
+              block.call(Regexp.last_match)
+            }
+          end
+          reset_text
+        end
+
         def parse_formatting
           {
             italic:    [email protected]('.//w:i').empty?,

spec/docx/document_spec.rb

@@ -206,6 +206,19 @@
 
       expect(@doc.paragraphs[1].text).to eq('Multi-line paragraph line 1same paragraph line 2yet the same paragraph line3 ')
     end
+
+    it "should replace placeholder in any line of paragraph using substitute_with_block" do
+      expect(@doc.paragraphs[0].text).to eq('Page title')
+      expect(@doc.paragraphs[1].text).to eq('Multi-line paragraph line 1_placeholder2_ line 2_placeholder3_ line3 ')
+
+      @doc.paragraphs[1].each_text_run do |text_run|
+        text_run.substitute_with_block(/_placeholder(\d)_/) { |match_data|
+          "_replacement_#{match_data[1]}"
+        }
+      end
+
+      expect(@doc.paragraphs[1].text).to eq('Multi-line paragraph line 1_replacement_2 line 2_replacement_3 line3 ')
+    end
   end
 
   describe 'read formatting' do