codeBlocks in options-file not working

Though I believe the initial issue of defining codeBlocks in the options json to have been resolved in #327, I have not been able to get my email platform (Listrak) merge tags to work properly.

From my `options-file`:

```json
"codeBlocks": {
"ltkMerge": {
"start": "<<",
"end": ">>"
}
}
```

HTML:
```html

Dear <>,

(where `basic information` is a field group, `firstname` is a field, and `default` is the fallback value if blank)

Out:
```html

Dear <>,

Is this because these tags live inside another semantic element? This will be the case 100% of the time since they are only placeholders for a text string. Or is the issue that there are other chars `\` and attributes allowed inside the `<< >>` tag itself?

Start by reproducing the reported output with the shown options-file codeBlocks configuration and HTML containing the Listrak merge tag. Trace how codeBlocks and tags containing backslashes and attributes are parsed, then verify that the merge tag remains intact while ordinary HTML is processed correctly.

Written by the indexing model from the issue text.