ArcGIS Arcade Labeling When Text Includes HTML Reserved Characters

Question

I am using the following expression in an ArcGIS feature label:

"(CH<SUB>4</SUB> " + $feature.Methane + " ppm)"

This works (e.g., CH₄ 15 ppm) unless the $feature.Methane value is "<1". In that case the result is

CH<SUB>4</SUB> <1 ppm

How do I get around this?

Answer 1

Some symbols such as <, > and " must be encoded similar to how it's done in XML or HTML. So rather than just typing the actual character, use <, > and "

In your example:

CH<SUB>4</SUB> &lt;1 ppm

lt stands for lesser than, gt for greater than

Answer 2

When using Arcade for labeling, the output is interpreted as HTML. In this case, the HTML reserved character < is in the field value, and its presence is messing up the HTML interpretation and display of the field value.

Knowing that Arcade labeling is interpreted as HTML, one can create a label expression that encodes the HTML reserved characters to their appropriate HTML entity.

var htmlEncode = Dictionary(
    '"', """,
    "'", "'",
    "&", "&",
    "<", "&lt;",
    ">", "&gt;",
);

var rawString = "Value <1 or >5.  It's me.";

for(var char in htmlEncode) {
    rawString = Replace(rawString, char, htmlEncode[char]);
};

return rawString

returns

Value <1 or >5.  It's me.