How to understand fontconfig output: "Pattern has 38 elts (size 48)"

When running with verbose output, and sometime even without, the first thing fontconfig writes about any font is a line like the following:

Pattern has 38 elts (size 48)

What do these numbers represent? And are they used for? After looking in the source code I believe "elts" is short for elements, but I still don't know what the numbers mean and if they are relevant for understanding the behavior of fontconfig. Below is a full example of output (with some of the charset lines removed):

-shellsession
$ fc-match "DejaVu Sans" -v
Pattern has 38 elts (size 48)
		family: "DejaVu Sans"(s)
		familylang: "en"(s)
		style: "Book"(s)
		stylelang: "en"(s)
		fullname: "DejaVu Sans"(s)
		fullnamelang: "en"(s)
		slant: 0(i)(s)
		weight: 80(f)(s)
		width: 100(f)(s)
		size: 12(f)(s)
		pixelsize: 12.5(f)(s)
		foundry: "PfEd"(w)
		antialias: True(w)
		hintstyle: 1(i)(w)
		hinting: True(s)
		verticallayout: False(s)
		autohint: False(s)
		globaladvance: True(s)
		file: "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf"(w)
		index: 0(i)(w)
		outline: True(w)
		scalable: True(w)
		dpi: 75(f)(s)
		scale: 1(f)(s)
		charset:
		0000: 00000000 ffffffff ffffffff 7fffffff 00000000 ffffffff ffffffff ffffffff
		0001: ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff
(w)
		lang: aa|ab|af|ar|ast|av|ay|az-az|az-ir|ba|bm|be|bg|bi|bin|br|bs|bua|ca|ce|ch|chm|co|cs|cu|cv|cy|da|de|el|en|eo|es|et|eu|fa|fi|fj|fo|fr|ff|fur|fy|ga|gd|gl|gn|gv|ha|haw|he|ho|hr|hu|hy|ia|ig|id|ie|ik|io|is|it|iu|ka|kaa|ki|kk|kl|ku-am|ku-ir|kum|kv|kw|ky|la|lb|lez|ln|lo|lt|lv|mg|mh|mi|mk|mo|mt|nb|nds|nl|nn|no|nr|nso|ny|oc|om|os|pl|pt|rm|ro|ru|sah|sco|se|sel|sh|shs|sk|sl|sm|sma|smj|smn|sms|so|sq|sr|ss|st|sv|sw|tg|tk|tl|tn|to|tr|ts|tt|tw|tyv|ug|uk|uz|ve|vi|vo|vot|wa|wen|wo|xh|yap|yi|yo|zu|ak|an|ber-dz|ber-ma|crh|csb|ee|fat|fil|hsb|ht|hz|jv|kab|kj|kr|ku-iq|ku-tr|kwm|lg|li|mn-mn|ms|na|ng|nv|ota|pap-an|pap-aw|qu|quz|rn|rw|sc|sd|sg|sn|su|ty|za(s)
		fontversion: 155320(i)(s)
		capability: "otlayout:DFLT otlayout:arab otlayout:armn otlayout:brai otlayout:cans otlayout:cher otlayout:cyrl otlayout:geor otlayout:grek otlayout:hani otlayout:hebr otlayout:kana otlayout:lao  otlayout:latn otlayout:math otlayout:nko  otlayout:ogam otlayout:runr otlayout:tfng otlayout:thai"(w)
		fontformat: "TrueType"(w)
		embeddedbitmap: True(s)
		decorative: False(s)
		lcdfilter: 1(i)(w)
		namelang: "en"(s)
		prgname: "fc-match"(s)
		postscriptname: "DejaVuSans"(w)
		color: False(w)
		symbol: False(s)
		variable: False(s)